[Malcolm]

I would suspect that most replicas use ali tanks and not fuel cells predominantly for the reason that the kit designers wanted to keep cost down and so designed their cars that way. Certainly that is what I would expect from a UK perspective. With GTD's if any have a fuel cell, that would have been down to the builder not the factory. Not aware of KVA, Tornado, MDA, Dax or Southern GT doing anything differently either.

On RCRs with their ali mono design, am I right in thinking the tanks are effectively part of the chassis? Or do they insert a bladder into the sills to form the fuel tanks?

If you want to save weight then a fuel cell has to be lighter which for competition cars is always desirable!