You can do that as long as you have a substantial substructure. The idea is that if you were to get hit the other car or barrier could not hurt you.
Example: If I was to kick your car hard and my foot did not make contact with you, then it is likely OK. If my foot was to go through the siding then you need to think of something stronger.
Remember to, we race in the rain and through puddles fairly often, you do not want your car to disolve.
Yea, that wouldn't be good... but we've made a sample of one that was at least 14 layers of paper and we could hit it with a hammer and it would not break.
For the papiermache be sure that it is well sealed for the reasons the 'Electrathon' listed. The rules say that the body can not be made of anything lat looses its strength when it gets wet. When you hit it with a hammer was the distance between supporting framework about the same as it will be on your car?
Yea it was. I think that it wont weaken even if it gets wet, just as long as we do a good job at it... with the paint and all the layers of paper we're putting on I don't think the water will even get the chance to weaken it.
I have experimented with polyester resin (used in fiberglass production) and different materials for reinforcement.
In one experiment, instead of fiberglass cloth, I used two layers of ordinary cotton muslin cloth I bought at a fabric store. I laid the two layers of cloth on a sheet of waxed formica and rolled them down with the resin. After it cured it was a very lightweight sheet (much lighter than regular fiberglass), smooth on one side, and easy to cut with tin snips. I had intended to use it on my latest car build, but determined I wasn't happy with the strength in regards to puncture resistance. I am going to try the experiment again, but I will use 3 layers of cloth with the center layer laid diagonally to the others. I may also try polyester double-knit fabric as I suspect it may be more puncture resistant.
Another thing I tried was 8 layers of ordinary printer paper (old student tests & worksheets) saturated with resin. This is similar to papier mache except it's waterproof. The problem with this was it was prone to trap air bubbles. The resulting product was less than 1/16" thick, very light, and very rigid. This stuff is good for flat panels, but if it needs more than a gentle curve it would have to be molded to shape; bend it too far and it cracks the resin on the surface.
Ok! That would be quite the experience...