Solar panel install

I'm getting ready to install a couple of Renogy solar panels on my EPDM covered 3/8" plywood roof. Because of space required, I have to place them near the front where the wind force will be highest. Their website recommends well nuts (expansion nuts) for use on RV roofs rather than the self tapping screws they actually provide with their mounting brackets. Has anybody used well nuts to attach brackets to the roof? I'm going to use six brackets per panel rather than the usual four, but am still nervous about how well they'll hold. Any suggestions would be appreciated.