It's probably going to be a long time before you realize that your roof has been leaking from solar panel mounting bracket screw holes - and by then the damage could have been extensive - including mold growth within your roof insulation.
What I do know is that in these forums post after post talks about periodically redoing all roof seals around air vents, air conditioners, antennas, refrigerator vents, etc.. The posters say "it's just a matter of time" before leaking will occur. How is one going to (easily, inexpensively, quickly) reseal all of the solar panel mounting bracket screw holes in their RV's roof - even if one can get close enough to each screw hole?
It's for this same reason that I refuse to have solar installed on our home's roof ... solar panels maybe mounted on poles in the ground out in our meadow would be ideal - but on our home's roof ... definitely not.
If your RV's roof is smooth material, Very High Bond double-backed tape hold down of the panel mounting brackets seems like the only way to go. By the way ... wouldn't the non-metal/non-fiberglass material under the soft sealing material (rubber or otherwise) on some RV roofs be even more susceptible to eventual leaking around screw holes?
