Phoenix Mesa (AZA) actually has a virtual aisle (download the app). https://www.emeraldaisle.com/locations It's a corporate location co-located with Alamo, and since Mesa is an Allegiant hub, they are actually a fairly decent size operation. Most of their business is Allegiant Alamo leisure renters.

I agree with the other posters, at least reserve a full size (since as an EE you'll pay mid-size), or a premium if you can afford it. It may look more expensive initially while booking, but the mid-size price will show for a full size reservation on the last reservation screen. If you reserve a premium, you'd pay the normal full size price.

Last time I rented there I got in ultra late, so couldn't use the virtual aisle, and got a PCAR on a PCAR reservation as an EE, which I had to wait for while they got it from Enterprise. Be prepared to leave with what you reserved if they're busy. Rentals earlier in the day there seem to have a better chance of scoring an upgrade, as well as rentals on a non-busy day for Allegiant. Tuesday, Wednesday, and Saturday pickup would be your best chances.