I paint lots of tubing each year.
I use .97cent wallmart paint. Other than the orange and red it kicks ass.
Look here to see the blue under a buck wally paint.
http://www.nw-wheelers.com/forum/showthread.php?t=57407&page=12
I notice allot of folks building/selling bumpers, axles, cages etc, dont paint them. Thats up to you to do. Cmon a 400 bumper and no paint? a 2500 axle and no paint?
I paint everything. Otherwise guys take it home and it rusts before they ever paint it. It only costs me 1-3 dollars to paint a job to ensure it wont rust.
MANY MANY times I have been asked about if I paint the product at hand, I say yes with wallyworld cheapo paint. I then get a dirty look and I instantly know I am dealing with a "spray paint pro".
They then spend the next half hour trying to convince me that the baddest ass $7 a can rustolonorite whipzam paint is the **** and it is all that is going on their cage/bumper.
I just step back and watch them lay on the nasty stinky run you out of the shop goodness they bring. The **** is so caustic it will make you gag and it will float around and stick to anything
Then after they get tired of cussing at the "fish eyes" and wrinkles of it lifting old paint I get out the .97cent garbage and spray right over the mess they made.
In dissbelief they watch dollar paint stick to grease, oil, dirty tube, dirt, pitch, etc.
I laugh in the face of expensive paint. It just gonna get smeared on a tree anyways.