I recently read on a board about who was rebuilding his bike. Once the frame was stripped down, he said he covered it in POR-15 then Rustoleum. Said it was tougher than powdercoat.
I've never worked with the stuff. Could you paint on POR-15?
I have used this stuff a lot with old cars, and yes, it is very tough, possibly tougher than powdercoat...but you have to follow the directions implicitly!...and there are lots of them! Very important to prep the surface...absolutely no oil contamination...a slightly to very "toothy" surface is better than a smooth one for good adhesion. It is tricky and messy to spray, easier to brush on. If it drys on your skin, uh oh, I've seen tattoes that don't last as long! Also there are special instructions for painting over it and it is not uv resistant, appearance will degrade but not the coating itself. Basically, it is a pain in the a. to use properly, but very effective for certain applications...also very $$$$.