On my trailer, I can walk anywhere (except on the AC, vent fan cover, etc.). I weigh 200#. The base material of my roof is a thick plywood, and the curved shape gives it increased strength.
I am also a big guy who also works on the roof occasionally. To be on the safe side, I use a couple of scraps of plywood to distribute my weight a bit.
Have someone hold the ladder as you get up on the roof. That person can also hand you tools. Get on your knees. Knee pads or a garden foam pad will make the job more comfortable. Shouldn't take that long for repairs. Your helper can hold the ladder as you get down. Then go camping!!
I went up on the roof yesterday to inspect the vent in the middle of the roof. I used a couple of extra bookshelf boards that I had laying around to help distribute my weight. I actually found a small crack in the plastic vent so sealed it with Liquid Nails silicone sealant:
i went up on mine to rebuild the roof vent it was brokwn and the local rv shop could get the covwr for 174.90 and the crank for 48.00 so i opted to build my own and covered it with a wood frame and plexiglass worked well. i didnt plan on using it anyway so now its a sky lite.
i was amazed at the fact that i didnt need to seal up alot of things but i went around the vents and antenna and a/c unit anyway with clear flex silacone .
The only product I would use around vents would be Dicor self leveling sealant. Silicone is a bear to get off and doesn't provide any UV protection. Due to the age of your unit I would take out all your windows and reseal with butyl tape and on the exterior with Lexel caulk. See my post of 7-31-2012 removing window for resealing. Should you need any HiLo parts call Jay at Mantelli trailer sales.1-716-625-8877. He is the parts manager and has years of extensive HiLo experience. They will ship parts anywhere.