Anyone tried to rustproof they car?

Haven't done inside rockers yet. The end cap on the forward end of the rocker where the inner splash shields for fenders attach has a hole. That's where I plan on going thru. I bought 4 cans. Used one just for the inside of the rear frame rails. As I said it is messy and will run anywhere there is an opening. It seems like I remember there being "drains" on the bottom joint along the rockers, but not 100% sure on that, haven't looked that close for a while.