How does one get to the seams, vents, etc. on top of the trailors?I use a wood, foldering type, step ladder and place an old throw rug over the top as a cushion and lean it against the trailer at a spot where a rib exist or near the edge near a window. At a point where some strength exists to insure I don't push in the skin. I also mount the step carefully. A 6 or 8ft ladder will get you to the top. In most cases you can lean over from the ladder and do the work you want to do. However, you can crawl on top but make sure your weight is over a rib or point of strength. Don't recommend kneeling. If you have to, use some heavy cardboard or similar. As no one sees the very top of trailer you don't have to worry quite so much about scratches. When on the trailer watch what you do with the toes of your shoes and if you are from Texas don't wear the metal tips on your boots.
Roy