When I had a 24-foot bumper pull, I had the time and energy to wax it once in the Spring and once in the Fall before it went into outdoor, uncovered storage. I now have the time, but not the energy to wax our 36-foot 5th-wheel. Just too much real estate to tackle.
I have it professionally washed and waxed each Spring and I wax the front cap myself in the Fall. I do just the front cap because it faces directly South, the back faces North, and the sides are partially shaded by neighboring trailers.