We had six panels (4 80s and two 125s) on the roof of our trawler, a very similar installation to any RV, but bigger. We used custom-fabricated omega mounts (similar to s-mounts but stronger) that held the panels off the roof for ventilation (per manufacturer's recommendation). We used self tappers but the recommendation elsewhere in this site to use rivets sounds good. If you have a fibreglass roof (as we did) then use 3M 5200 or similar adhesive bedding/sealing compound under the mounts, not self levelling compound. Self levelling compound is not an adhesive. We also put self levelling compound right over the mounts, perhaps not needed with the 5200 but why risk a leak! We never had a moment's trouble with this installation, despite going through some heavy gales and taking sea water right over the boat on several occasions.