As air moves over the rear cap, (assuming you have air foil), it is forced down, the FMCA decal distorts this airflow and causes a second air dam effect and vibration which makes the screws loosen because of this vibration. Since you are X amount of feet forward of this vibration, you most likely don't hear of feel it. Put some clips on the FMCA decal so it can be easily removed from the ladder, and make removal one of the things you do when leaving for a new spot/trip.
Assuming you have the 1/4x 20 screw w/large flat washers, holding down the A/C cover, you can put a little lock tight on the screws holding the A/C shroud down. Use the color which allows the screws to be removed if necessary. I believe it's the blue bottle, not the red one. See it that helps.
FWIW - Please add a signature to your posts so we have year/model, etc for the coach, as this helps when asking for information. You can do something like mine if you wish.
Monty & Janet - 2007 Alpine APEX 40 MDTS
S/N - 75715 - Retired - Master Certified RV Tech