I used a three step ladder / stool to get up on the bunk end. Kneeling on the bunk end on top of the canvas I was easily able to reach up and install the Velcro. I left the mattress in place. I would advise zipping up the window flaps and removing Reflectix panels (if you have them) first; my knee kind of bent the Reflectix a bit but no issue with the canvas.
The tape appears to hold very well. By running the Velcro continuously from one side to the other I figure it is very unlikely to lift. The PUG reaches slightly wider at each end of the Velcro. Although I have not had mine in place for too long, the Velcro appears more likely to lift rather than the adhesive.
This is the type I used in it's full 2" width, one roll per bunk end, black colour. It is rated for outdoor use.
Velcro | Velcro Industrial Strength 10 ft. x 2 in. Tape | Home Depot Canada