Fat bikers....are 27.5 really a thing?

Good luck getting it right. As others have said wide non specific tape is probably the best solution. I use clear gorilla tape. No idea why clear - must have read it was better at some point!

I've mentioned it before but clean the inside of the rim. Then clean it again. Maybe again! Isopropanol alcohol is your friend here.

My method, found on YouTube somewhere.

1. Install normal rim band of colour of you choice to match frame or whatever.
2. One wrap of gorilla sticky side out over the middle covering the rim band overlapping by 100mm or so
3. One wrap of gorilla stick side down to the left up to but not over the rim wall/hook overlapping by 100mm or so
4. Pause and squeeze out all the air pockets
5. One wrap of gorilla stick side down to the right up to but not over the rim wall/hook overlapping by 100mm or so
6. Pause and squeeze out all the air pockets
7. Then go over the air pockets again, then again.
8. Carefully pierce for the valve
9. Use a P nut - with my rims at least normal valve an nut combos just don't cut it on flat single skin rims.

So there you have it - with my rims and Surly bud/lou combo actually inflating is a bit of a ballache with a compressor and a luggage strap as they are so baggy but you don't seem to have this problem.

The above might sound a pain...and it is a bit...but promise it's worth it.

If you don't have any luck taping it and getting it to seal, you could look at fatty strippers - essentially a nicer version of a split tube/ghetto tubeless setup. Not sure if you can get them easily in the UK though.

I did my mulefat 80s with a 24 x 2.4" split tube for a while this winter and it worked great!

Use a P nut – with my rims at least normal valve an nut combos just don’t cut it on flat single skin rims.

I had to use these too as the standard valve nut just wouldn't tighten up enough on the single wall rim (I don't think the valve was threaded all the way down). Other than that, tubeless went pretty smoothly for me and the JJs don't seem to bleed air. FWIW I think I have 200ml of sealant per wheel.

Yah I had similiar issues with some valves, the "plug" basically has to pull a little bit through the rim to seal. It was a wee bit fiddly, I couldn't just use a random washer, it had to not be flat against the valve hole for the same reason. Canti/sram brake washer worked out perfectly (the concave one)