Fill it with whatever your favorite or easily obtainable non shrinking, sanding filler you have (that is safe for plastic). I use Aves, some guys prefer bondo, others Milliput or Squadron putty. It's all good.

Tape would be fine as a backing to hold, you may want to back it with something solid so you don't push through. If the hole is wide, you can throw some wire or screen to help the putty hold. Make sure you get it tight around the edges for a good hold. You can rough up the inside edge for a better bond.