I've found Fantastic Fan has excellent customer support. Might want to try contacting them???
Maxx Air vent covers cannot be used with Fantastic Fans with automatic lids like yours. The lid will be either fully open or fully closed... Maxx Air covers won't allow the lid to fully open. They also restrict the air flow with FF's.
Ultra Breeze vent covers are designed for Fantastic Fans which I use but my fans don't have rain sensors so the lids are manual but even with these covers the lid will open fully but it still butts up against the cover.
Personally.... I do not rely on any sensor to work flawlessly when I'm not around so I would, like cfiowa suggested, leave them closed when not there.
2014 Chevrolet Silverado 3500 LTZ CCLB DRW D/A - Transfer flow 40 gallon Toolbox/Tank Combo - Line X - Edge Insight
2015 Palomino Sabre 33CKTS - Platinum Edition - Progressive Industries EMS HW50C - JT Strong Arm Stabilizers - Ground Control 3.0