Ideas to cover middle roof vent hole for a week or two?

[RipNC]

Need to cover the 14x14 middle AC/vent fan hole for a week or two without screws.

Backstory:

FedEx Ground damaged 2 new Coleman Mach 3 PS units (drivers had them on their side while transporting and the compressor weight bent up the bottom pans). UnitedRV.com was great, but they aren't willing to ship a 3rd unit and I don't blame them 1 bit! I need to return the first unit (installed w/o opening the cover) and source a unit that i can pickup and inspect (before purchase). I don't want to screw the old fan back into place since I've cleaned the area and coveredall the holes with Eternabond tape. Not sure if some sort of plastic panel and tape (Gorilla, Duck, Duct or foil) wouod hold up to a bad t-storm or not. Sure don't want to learn the hard way.

Anybody done this?