fitting solar panels

hi there,
we are looking to fit a large 150W solar panel in a frame to the roof of our caravan. We have different opinions from various people on the best way to fit the frame for the panel. Some say, use 227 sikaflex and don't screw into the roof, which I am not sure would hold the front down whilst travelling with wind being able to get under the front and cause the panel to either come loose or flip, other say affix by glue and screw....
I am not keen to screw into the roof either, as this could cause problems later down the track with leaking.... Any suggestions would be appreciated Cheers happy travellers.... :)

Kerri, QLD