Hi.
This is a long reply to your post and for that I apologise. If you want to cut to the chase, I have never used a fuel cell only a fuel can, but I no longer even do that, I just manage with the 200 miles the standard tank will take me. I have fitted a BMW tall screen to my R1150r which reduces rider fatigue but turbulence hampers high speed travel.
The rest of my post is about how I came to my decision about not carrying auxiliary fuel and some wider thoughts on motorcycle travel. These are just my thoughts and not a suggestion that you should do likewise. My travel experiences have been restricted to western, eastern and southern Europe. I don't know anything about the geography of your area.
I run a Yamaha XT600e along side my R1150r as a sort of sacrificial winter bike if that makes sense. It is also modified in a number of ways for travel/camping/exploring, one being a long range fuel tank which sits exactly where the standard tank should, it's just bigger. The last tank of fuel took me 324 miles until I hit reserve.
Like you I would love to have a longer range on the R1150r and I have contemplated various ways of achieving this, however I always came back to the same most economical and practical solution-plastic fuel cans. Strap them on and then decant them if/when necessary into the main tank. Unlike custom fuel cells they cost very little, they don't require plumbing in, they are readily available in a choice of colours (I prefer black), when empty they weigh almost nothing, you have the choice to travel with or without them, they are easy to carry when walking to find a petrol station, they are easy to decant into other vehicles or camping stoves and you can pass them to another motorist to go and get you fuel on your behalf. Each standard 5 litre can takes you another 50-60 miles, so with two on, you're knocking at the door of true expedition mileages.
The disadvantages that occur to me are; they don't look pretty, they must be empty to board ferries, and I don't believe they will pass scrutineering for organised long distance riding events like Iron Butt.
I have however, stopped carrying them as well as worrying about fuel range for reasons I will explain.
I live in the UK, specifically in south Wales, and last July I decided to ride to Spain for a holiday; a return trip of just over 3200 miles. I wanted to use some of the same routes through the Pyrenees that the Tour de France riders were going to use (they always use some of the best and highest) as well as explore some of the more remote mountainous areas of Spain. The plan was that I would spend five days riding down to Alicante and my GF would fly there. We would spend six nights in a resort then ride back together, city hopping on the way. (Barcelona, Paris etc). On the day of departure I packed the bike ( it is fitted with BMW panniers and a large Givi top box) with all my clothing, GFs clothing, two sets of wet weather gear, GFs helmet and bike gear, all our camping gear, tools and all the other paraphernalia that one takes when touring; and to my dismay I just couldn't fit my fuel can on. At first this bothered me because I knew that for a time I would be travelling in the lesser populated areas of Spain, however I stopped worrying about it and focused on a couple of things I have learned over the years when motorcycle travelling.
1. In Europe you are rarely ever more than 50 miles from fuel, you have just got to know in which direction it is and for that God/Allah/U.S Military/Flying Spaghetti Monster whichever you believe in, gave us Sat Nav. (Still need maps though).
2. When you break down or run out of fuel or suffer some other mishap, somebody always comes along and helps. Sometimes it's immediately, sometimes it's half an hour or half a day, but somebody always turns up. This is because of two things; firstly you are unlikely to be travelling a route, on a R1150r at least, that others don't travel, a tourist, a mother on the school run, a retired couple going shopping, or a farmer, or just some regular guy going about his business; And secondly, in the main, ordinary people, regardless of age, nationality, colour, religion; like and want to help others. I accept that you could be unlucky and get taken advantage of, or even murdered; but statistically it's not likely. I think we worry too much about these things because of the countless B movies we have watched. You know, where the college kids or the young couple take the wrong turn and ask for help and the rescuers turn out to be flesh eating hillbillies, their condition caused because of drinking from a poisonous underground water source that is at first believed to have been infected by toxic waste dumped by a contractor working in cooperation with a corrupt local government officer who is himself on the run from Mafia hitmen because he's absconded (by canoe) with their share of the money. All of whom are going to be whacked by the CIA agent gone bad who has discovered (in a long lost WW2 file that was hidden in a packing crate in a humongous military hanger), the map coordinates of the lost U boat carrying Nazi Gold from Germany, that is stranded in an underground lake with its batteries leaking into a natural spring that feeds the well on the farm of the hillbillies blah blah blah.... Actually I might have combined a few film scripts into one there and possibly made some stuff up, but you get the idea. Hollywood doesn't make many films where the tourists don't run out of fuel because they're never far from a petrol station, or if they do, a friendly farmer comes along, gives them a lift to the nearest one or gives them fuel from his emergency supply in his barn, and then gives them a lift back and waves them on his way. Movies are made to make money and you're not going to pack the cinemas out with that story line are you? However the Nazi gold, flesh eating hillbilly thing.....I might have something there. What I'm trying to say is that we are all massively influenced by the media we are exposed to and it warps our perception and can limit our travel experiences.
Please excuse the vernacular, but when travelling, sometimes, 's**t happens'. But it is rarely something you can't get yourself out of.
Last year when travelling along an old drovers road, I lost concentration, skidded, and came off the road down an embankment and ended tangled up in the bike with my hand trapped between the wheel and the swinging arm. I knew almost immediately I had broken the back of my hand. I had been travelling with another motorcyclist but unfortunately he was in another part of the valley and didn't know where I was or what had happened. To make matters worse, I was out of sight, laying among greenery, dressed in green and unable to reach my mobile phone (there was no network coverage anyway) I had a decision to make, was I going to be rescued or be my own rescuer. I chose the latter. I forced my hand out from its trapped position, breaking my wrist in the process. Unable to pick up the bike because of my injury I wondered what was going to happen next, a long walk perhaps. And do you know what happened? Somebody came along and helped. A random guy travelling the same route by car caught a glimpse of me and stopped. He alerted the other biker to my predicament and then once the bike was upright I rode it out of there. Four hours of clutchless gear changes later I got home. X-rays at the hospital confirmed a broken left hand and wrist. No biking for six weeks and plenty of time to contemplate stuff like why do I do this overseas motorcycle travel thing. I know I learned one thing from the experience, when the chips are down you dig deep.
So what went wrong on my Spanish trip, how many miles did I walk, any broken bones, flesh eating hillbillies, u boats? As it happens, none. On this particular journey my 3200 miles passed without mishap although I did ride quite a few miles with the fuel light on a number of times. It was a great trip, a great riding experience, a great holiday. Now wouldn't that make a great film?
So that is why I no longer carry auxiliary fuel, firmly believe there's nothing to be nervous about and that its the twists and turns of motorcycle travelling that make it interesting.
I now think of the fuel stops I make as opportunities for engagement with local people, a chance to pick up a local map or tourist information, sometimes they are diversions off my planned route which take me to interesting places, campsites or restaurants I would otherwise have missed. When riding the XT600 with the long range fuel tank I don't refuel as frequently, but I stop just as often. The 200 mile range of the BM enhances the travel experience not detracts from it.
And if something does go wrong, somebody always comes along. You just got to hope they don't play the banjo!
All the best.