how would you go about making a mirror image of a 3D form like a fender or cowling? If it helps, these will be hollow parts or will be composed of such pieces.

my only idea so far is to make a set of cross-sections, form a crude jig out of those, use that to vacu-form the part and then reverse the cross-sections to make the opposite jig and make the flipped version of the parts.

any suggestions?

Gday Paul
How about deleting this thread, and starting afresh with a new title?
Something like "vacu-form help needed" etc... This may pique the interest of those who are in the know without them bypassing the thread...? Just a suggestion...
Sorry that I can't help you!!!
Cheers
Brad