The endcaps you would be looking to make for a '68 are compound curves, meaning specialized equipment would be involved to make them. The flat sheet construction of Airstream end caps went by the wayside with the 13 panel construction of the mid-50's. With each reduction in the number of panels that make up an end cap, the shape & "pattern" would change - each becoming more dependant on compound curves. The more panels the simpler it would be to make using cardboard or heavy kraft paper as templates. There are a couple of forum members that have added wood to their interiors, you may want to perform a search to see what you can glean from their projects.
Your best bet for a plastic replacement end cap is to either mend your existing ones or use them as molds to make new fiberglass ones. The last option would be to find a salvage yard with the same model you have and hope those end caps are in better shape than your own.
Good luck in whatever you decide to do ~
Shari
