IMO, screwing down the brackets is the best course. Depending on how your roof is built, screwing a 2" fastener into a wooden roof truss will keep anything from ever moving. I found mine by measuring back from a vent that was on a 16" center with the rest of the roof. A stud finder will also find the trusses from the top side. If location dictates that you fasten just through the roof sheathing, use shorter fasteners and more of them. Apply sealants under, over, and around the brackets.
Tip: If you fasten through a piece of Eternabond tape, the tape's adhesive layer tends to seal and cover the screw heads.
Eternabond's video on sealing screwsGood luck with the solar, I wouldn't worry one bit about wind unless you mount the modules more than 6" above the roof. Solar charging for an RV is one of the better things I've found in the last few years.
FWIW, the brackets for this 235W module hold a four way tilting mechanism and the module:
