I spent a long time (and quite a bit of money) messing about trying to get something suitable, following my abortive contact with the hovercraft mob. I tried a wide variety of inner tubes, ranging from bicycle (not long or wide enough) through motorcycle to cars; all these were too thick so you couldn't fold them properly to make the correct shape. Then a friend gave me a couple of original Ruby front seat squabs, and the tubing used is very thin rubber - much thinner than any motorcycle or car inner tube. I wasn't able to find any suitable tubing, so I eventually got a couple of Inflatable Stadium Seat Cushions from Putnams - these are fairly good, but not quite big enough. I solved this by making a U shape out of foam rubber seating material to fit round the sides and front of the Putnams cushions.

Some downhill mountain bikes now use quite fat tyre's almost MC section and in big diameters, the tubes for these must be quite thin as weight would be a big problem. I wonder if they could be suitable for adaptation? just a thought.

Location: Auckland NZ

For anyone experimenting, but without experience of, the technique is to inflate just sufficient to separate posterir from the seat base. if over inflated tend to roll about like a cork in a storm.

Location: Auckland, NZ

26" x 4'' fat mountain bike tube looks promising.

Location: Auckland NZ

Tanya and I stumped up the dough to buy the repro. ones from the hovercraft people 5 years ago and have never looked back. They fit perfectly, look just right and are very comfy. They are made of slightly different (more durable) material than the Moseley originals. If you can afford them my reccomendation would be to buy them.

The Ulster has custom made spring bases (with horse hair etc.) that look extremely good on the car but do cause some numb-bum on journeys over six hours.

The '29 saloon has £1.99 old style blue and red li-lo inflatable camping cushions/pillows that work really well. Only downside is that they make the base 'look' flat when not in use, some foam would probably sort that.

Finally, the Chummy has old 18" tubes (only because I had them spare) taped with stretchy tape to the correct shape and a thin layer of foam on top and around the edges. These are extremely comfortable but do look slightly lumpy when not being sat on.

well, what a treasure trove of possibility! My first experiment ziptie-ing the 17" gets something of the right proportion (but but not area), so I will now google Puttnams and fatty mountain bike tyres! Thanks all.

I can see that buying the proper things will be money well spent, but their ludicrous delivery charge just annoyed me and I feel that I need the perverse pleasure of finding something homespun.

I'd looked at repro inflatable interiors and gave up. A visit to Decathalon for some bike spares revealed they do a nice camping cushion for a couple of quid so I bought a couple and they just get moved from car to car.

These have been recommended to me by Pembleton owners as being very comfortable. Only a couple of puffs of air are required to transform a bum-numbing seat to luxurious comfort..
eBay item 272336914481

Location: Ripon

I recollect that when I was driving RPs around late fifties/early sixties the original cushions were still serviceable, even if they needed occasional reinflation. Comfort was best when the outer 'square U-shaped' part was blown up fairly well with lower pressure in the centre part. The fact that they were made suitable for this technique was a very good feature of the design. The only modern replacements I have seen were not made with two seperate chambers, so they can never be so good.

Location: just north of Cambridge

I have cushions made by Bryan Purves in the Ulster Rep. Cost was 148 quid each. Gordy, if you have trouble with shipping, I will have a 20' container coming to Seattle in a couple of months and have room for some parts.

Location: Sunny Seattle

Location: New Forest

Like Erich, I had mine built by Bryan Purvis. They are two separate chambers and he also made the leather covers.
Unbelievably comfortable. Certainly not cheap but you do get what you pay for!
David B.

Location: N. Oxfordshire

Well, a 26" bike tube definitely provides enough length when folded in to 4, from trials with a standard mtb one. The 17 or 19" car tube does not, and is too thick in feel.

So have decided £13 for two is well spent to deciding whether the new 4" 'fat' ones have enough width/depth when semi-inflated. (its no good if you pump them all the way)

watch this space.

first results good. with some foam support around, they are strong yet pliable and cover the right floor area.
Just need to get the joining method right. Presently ziptieing in two places, but wonder whether one could use silicone sealant, or else just some cut up inner tubes to make the links without creating kinks.

this sort of thing, should you be contemplating...
http://www.ebay.co.uk/itm/Nutrak-26-Fat-Bike-Cycle-Inner-Tube-Presta-26-x-4-0-4-3-Multi-Buy-Saving-/182187317902?var=&hash=item2a6b35da8e:m:m3dra0Ei3DW3S8tILeRv19g

Sorry Jon, the pictures of card boxes doesn't help!

Location: Near M1 Motorway Jtn 28

Duct Tape maybe? But wonder if you could glue wide strips of inner tube with puncture repair adhesive to bind them, this would stretch and give with the tube, provided the adhesive was strong enough. Perhaps experiment with an old tube first!

Location: Auckland NZ

I can recommend self bonding repair tape for this job - it stretches.

One has appeared on sBay, item 272439134817

Location: Ripon

I also have hovercraft seat cushions in my Ulster. But they are not as comfortable as original ones in my chummy.

Location: Vancouver Canada