If your trunk is getting wet it is more likely from the rear window channel than the trunk lid weather stripping. This is common on old GM's. Lay in your trunk with a flash light and look close for signs of water/rust. You will have to remove the rear glass and clean and repair the channel. After 1967 Chevy stopped using model specific window gaskets, and instead used a generic type "window ribbon". This is readily available, inexpensive and relatively easy to install, but the key is in the preparation. The channel must be straight, solid, and clean. Depending on how bad it is, this can be a major repair.
I have used the por-15 floor patch kit you mentioned and was not happy with it. The coating needs to be applied to a surface that has been cleaned / prepared with several products according to specific instructions, with little room for error to work properly. Then it needs to be top coated again otherwise UV rays will damage it. Plus when you reseal the open cans, they become all but impossible to re-open at a later date. I literally bent and twisted cans into almost unrecognizable shapes before the mangled pos would finally tear open. What a big PITA.
If you don't need/want to replace the floor then clean it off with a wire wheel on a drill and use this product instead:
http://www.eastwoodco.com/shopping/p...ProductID=1130
Auto Restorer magazine tested it against POR and thought it was better too.
If there are large holes you need to make repairs with metal. It doesn't need to be fancy, just pieces cut to fit and fastened with short sheet metal screws. If there are small holes, just lay fiberglass mats and resin over them. Do this after the Rust Encapsulator has been applied and is completely dry. Fill any seams with seam sealer made for cars. This is also available from eastwood and is applied with a caulk gun. After this you can spray the entire trunk with trunk "splatter" paint from a rattle can.
You can (and should) do this yourself. You will save money, and gain a lot of valuable experience.
