I think I have found the perfect item to use for a fuel bladder...
The bladders used for hydration packs!
I luckly had an old one laying around and plugged the outlet hose and the filled it full of fuel and layed it with the fill cap down so that if any part will get "eaten" by the fuel, I'll know pretty quickly.
I'll report back on my findings soon!
What a great idea. Opens up all sorts of options. Could put a fuel tank in any thing. The coolest looking classic one, like your sayin Baird, the fake tanks. An old brass fire extinguisher, a Spider-man lunch box and just about any thing with no real alterations. Even make just a classic looking tank, but could be made from any thing, I am not sure about this but might not need to be vented. Would be safer in a crash.
I don't think this is the answer to any existing problem but rather just an alternative with some advantages for us.
Joaquin, I put gas in a laundry detergent jug for a year to see if the plastic would break down. Makes a perfect gas can with a button operated spigot. It didn't fail and has had 2 and 4 stroke fuel in it. Be really great to see your idea work out!