Simple items can be constructed by using corrugated cardboard covered in resin and possibly in fiber glass if more strength is required – remember resin is poisonous so get a good mask before trying this.
I used this once when I was younger to make a bicycle trailer – it was light and strong and lasted quite well.
and i am thinking of using the method to make a teardrop trailer – I also improvised a magazine once out of this but it didn’t work very will as the spring I used wasn’t strong enough – but I am sure this method would work quite well if i had used a stronger spring and it did feed the rounds, just not smoothly (for the record the mag lips were made of steel)
the produced magazine was rather fragile because of the fact that i used thin non-corrugated cardboard.
basically make the item you wish — out of cardboard – hold the item together with pins
then mix up a batch of resin ( used for body work repairs at panel beater shops ) saturate the model in resin by painting it on with a paintbrush.
let it harden over 24 hours and then put on a second coat… repeat until the model is strong enough for your purposes. i find 3 layers is usually enough without getting too thick and loosing detail. but you can upscale this many times and make the cardboard as thick as you like by laminating it.
Also now its water proof 😉
To add even more strength you can then use fiber glass sheets to cover the item before the last coat of resin is applied ( so it still sticks )
and saturate the fiber just like working normally with fiber-glass, but this time you just don’t need a mold.
Apply clear coat if you like – for a fine finish – or camouflage – what ever floats your boat … oh yeah can make boats with this method as well ..
To make a tear drop trailer – make the trailer frame out of the cardboard by laminating multiple sections and cover in fiberglass, the rest should be very obvious, the nice thing is its easy to change and easy to build a mock up and laminate multiple boxes to provide strength.