Ive weighed this option many times. To the point i ordered the access cover. Just havent done the access yet. However i have used a hole saw in fiberglass dashes on numerous occasions. I would suggesst running the drill in reverse using lite pressure untill the gel is “scored” before running the drill in forward. This will prevent “chipping” on the o.d. of the hole.i would also remove the sharp edge around the o.d. (outside diameter) of the hole. This serves 2 purposes. It will protect your arms from cuts. It will also reduce the chance of cracks coming from the sharp edge. A roll sander does a nice job for this application