My C20 has the original bed wood and black paint. I touched up the bare spots using a mixture of lampblack and linseed oil as was done by GM. Now I am wondering what to apply over it to protect both the paint and the wood. I was thinking of using a marine varnish but is there a another product for this purpose?
Best thing to do is to get a length of new wood. Use the same mixture that you touched up the bed and do the whole board.
Then mask off the board into sections and try different finishes that you will like. Then leave the board outside to be exposed to the weather and see which one is the best.
