Parking car outside for about 2.5 months

The EPA has required EVAP systems since 1971. Any outside air would get "strangled" through the charcoal canister. But like I said, I haven't had any problems, and OP's car can only be tighter.
I dont think you understand the evap system takes air and fuel mix inside your tank and passes it thru an activated charcoal canister that absorbs the fuel vapor. That has nothing to do with the air that goes IN to your tank as fuel is consumed. That out side air has moistue that condenses out. ALL FUEL TANKS HAVE THIS IF THEY DIDNT THE DECREASING VOLUME OF FUEL WOULD CREATE A VACUUM. LOOK IT UP!!!
So please explain how a parked car gets more condensation that causes problems vs a driven car. It's parked! Gas isn't going anywhere, air doesn't really want to get in. Gas caps have a valve that requires a certain PSI to overcome. Between zero and that PSI, air isn't getting in or out of the tank via that route.
I had to check the title again.
So you all worry about a vehicle that sits for 2-3 months?

Anything less than 6 months, I would not do anything. Park it, lock it and leave.
I don't have an issue with mice and such, so if that is an issue in your area, then sure.
If you have an older battery or something that uses a lot of power sitting, then a solar battery tender could be useful.