Hi Goinstraightup;
I just made some test parts for glass-filled nylon motor mount rails. They're really made for the profile planes and CA glue or other adhesives (for foam bonding), but could be bolted into place as well.
The test parts are 3/8" X 3/8" X 12" and 3/8" X 5/8" X 12". They weigh a little more than hard wood, but no hole enlargement from vibration and no soaking up oil!
Might be something someone might like to try.
Send an e-mail if interested. I'd like to have a test case to check them out.
(PS - we might call them "KrazyRails" - he, he[X(])
Ray