Thanks for the replies. I like the look of satin, but wanted to know if the gloss was like house paint and better in the long run. At least I know, but I still think I will go with the satin. With a base of POR15, I think it should be OK.
POR15 is the ticket! It really won't matter what you put over the top, in this case it's what's underneath that counts
There's a picture someplace here on the forums where someone had painted the tongue, rear bumper and wheels to match the tug. The trailer was white. Looked nice and it's one way to "match" the combination. Just something to think about.