Interesting... I think that's a very important point. Having a sump for gas exchange. I don't run a sump (at least not yet). Mine is a 5g so that might determine the route I go. My tank is upstairs so heat can become an issue. I'm glad I asked you about this. Thanks!! This might help the OP as well.I have 2 cats roaming around so I went with glass.
On the rimmed tank there is a 1/2" gap on the back so it doesn't actually rest on the back rim. The tank is in my basement so no heat issues, and there is a sump+skimmer so no worries a out gas exchange; and as mentioned the fresh water condensate that forms on top keeps most of the salt creep at bay, I still get some around the top where the lid rests on the rim on the sides and front of the tank. I clean the top simply because of the cat hair.
On my rimless tank there is ~ 1/4 of an inch clearance on the sides, I keep it pushed to the front so there is ~1 inch open on the back of the tank