I just replaced AC unit with a vent on my Boler
13 and had no problem reaching all areas from a step ladder leaned against the trailer with some blankets to protect where ladder leaned against it.
But if you need to get on top, how about thinking inside.
Support the roof with some up-right 2x4 from floor to ceiling just like I do to support the 2 feet of winter snow in Maine.
I lay a 2X6 on floor then mesured height from top of this to ceiling, minus 1- 1/2 inches.
Cut as many 2X4 this messurment.
Then cut another 2X6 for the ceiling and wedge your 2X4 as uprights.
This will give you plenty of support to crawl up on your roof if you need to.