Evening Ron,
Hmmmmmmmm, rusting, again I wouldn't worry about it. By the time your tubing, new high carbon drill stem, decides it's time to give in and rust the water will be gone./w3tcompact/icons/laugh.gif
I would paint the outside asap though. That is important not only rust will attack the pipe but also everything you attach to it. The pipe will hold out for thirty years or more. The other stuff not so long.
I hope you're not like me. Painting is one of those chores I've found the perfect tool for, check book.
Seriously, for your pipe there are many options. One of course is the mitt. Another is the foam rollers. And another is the pipe rollers that consist of three little rollers in an arc top and bottom. If you have to paint the pipe and there's nothing welded to it like you have around the dog pen, the little roller is the ticket in my book. Mostly because you can clean it and reuse it. The mitt and the foam rollers are one shot items.
Even better is a HVLP sprayer. They lay down plenty of paint (you'll never find rust under a run). You aren't killing the environment like you can do with regular spray gun and compressor technology. And they are a lot easier than a brush when you're doing something like the dog pen.
Plus if you're so inclined you can find mama's good side because they do stuff like refinishing outdoor furniture better than just about anything else. Of course nothing beats the expertise you get and ease of use of the check book.
