eternabond and roof AC install

Sooooo, I'm about to install my Dometic rooftop unit, and I see the install requires pulling down on the foam ring around the AC. I'm thinking of using eternabond double putty under the foam. Anybody see any potential problems with this?
I'm also planning to install my Fan-tastic Vent using that tape too. That product says to use the included foam ring as the install sealant. I'm thinking the putty will be better.
Any advice?
What a charley fox-trot BTW. I bought my AC used, and never even thought about the piece inside. The vents, the thermostat, etc. So it's a return, a supply, and some wires hanging out of my roof till I get something to hook to that harness.
I'm also planning to install my Fan-tastic Vent using that tape too. That product says to use the included foam ring as the install sealant. I'm thinking the putty will be better.
Any advice?
What a charley fox-trot BTW. I bought my AC used, and never even thought about the piece inside. The vents, the thermostat, etc. So it's a return, a supply, and some wires hanging out of my roof till I get something to hook to that harness.
