why would you buy a gallon to paint a 8 ft piece of steel?
d's right on the inside painting. i take a rag tied to a wire, dip it in the paint and pull it through the tube, keep rotating it to get good coverage.

Thanks 4 advise, but I figure the tube will never get wet with saltwater and I do rinse the inside, I shoot hose right down openening by coupler. I only trailer 6-10 Times a year. I go 10-20 miles away max.

Whatever dude, you do what you want, but I think you're missing the point. IF you go anywhere near saltwater, then the trailer will get wet inside and out. We're not talking about dipping the trailer in the water, we're talking about the salt laden air surrounding the metal and leaving a microscopic thin film deposit of salt on the metal while you're out fishing. It's unavoidable, and I can tell you from experience that it doesn't take long to rot out bare metal. Now, if, on the other hand, you are only going to do fresh water fishing and will be bringing the trailer to a lake or river nowhere near salt air, then perhaps you can get away with not painting the inside... But I'll never buy that trailer from you.

Yeah I will paint it and use it. I don't plan on having this boat forever, besides I don't use the trailer much I keep the boat on a mooring most of the year. I will just save the old tube and when I go to sell the trailer I will put the old one back. Iknow I am cheesing out but I can't afford to put money into it right now. Thanks for input

do a little searching for a hot dip galvanizing company in your area... I once worked at one and if someone walked up with something like that on second shift and found their way out back we'd generally charge em about $20 to dip something like that n we'd buy pizza w the money