Anyone know of a good heavy duty coating for a rifle?

I'm wondering if anyone knows of a way to coat a rifle with something that is water proof and heavy duty. Essentially I want to put rhino lining on my gun. I have a bolt action .22 that I use for camping, but the problem is that it rusts like a bitch. I have no idea how or why, but even after i oil everything it starts rusting after a few weeks. Its a cheap gun, so I don't mind experimenting on it, but I don't know of anything that can do the job I'm wanting it to do. Paint and most other things will chip (unless there's some crazy paint I don't know about). Any ideas?