My brother is standing on my heels to finish the tricar and get busy on a velocar. He can see the purpose in building one since he would like to have it to scoot around our area while going to the store and this is a beauty. Thank you I.W. for supplying these and the language help.
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I had envisioned a plywood covering. They sell what they refer to as wiggle wood which is a very bendable one directional plywood. That is it bends on the horizontal or the vertical and is two layers of rotory cut 1/8" wood with a membrane in between. This can be rolled like heavy paper into a very tight roll. The wood looks to be like poplar or cotton wood.
It bends across the middle of the sheet for short runs and along the length for long runs. Glued and nailed to the frame I would then glue canvas to the plywood and make or buy a filler paste to fill the canvas grain much like they did with canvas covered cedar strip canoes.
Paste filler is available on line from furniture restoration suppliers and when used to fill the grain in wood it is coloured with an appropriate stain. It can be painted over as it comes in the can and only needs to be thinned out with paint thinner. A light sanding would be needed to smooth it out.
Not as inexpensive or authentic as cardboard and newspaper though.
Steve.