I have painted a few trailers and my truck camper and used single stage urathane paint. I used Genesis from Sherwin Willaims, and it is bascially a one coat paint.
there is the truck camper last year when I put it on my tow vehicle, there is a fifth wheel hitch under that camper too. That Lance is a 1993 and was that off white color, so i went with bright white and a couple of stripes.
Using base clear would be more expensive than single stage, more prepwork and double the materials. Single stage Genesis or Imron from Dupont, nice thick paint, its what we use on the big trucks, Kenworth Peterbilt and so on.
Not familiar with the Dicor your using, but thinking its not for the side of the camper, but one could do a little area and see how it turns out.
Also I have seen guys paint thier pickups with a brush and roller, heh don't laugh, they did such a good job that at a glance I could not tell the difference.
I had a Cardinal fifth wheel a few years back, after re doing the interior with new furniture and floors I looked at the outside and it was dull, the graphics were faded too. Masked it up and shop a coat of Imron clear on it and it came back nice and shiny. Took me a day to scuff and mask and then another half day to shoot it. Month later it burned down.