Corey,
Glad you were able to get an ACS mat. Regarding fit, I think you will be fine either way, there are two schools of thought. One group let the ACS mat overhang to gain better airflow under the mattress. Personally, I just trimmed it to fit my tent as my mattress fits very tight in the Columbus. I haven't noticed any condensation under the mattress ever. I think the idea of airflow under the mattress comes from marine applications where it is really damp.
Right now I'm rebuilding an old house in Portland and didn't want to find a temporary bed so I took the mat, mattress and bedding from the roof tent, built a platform from two sheets of plywood and made a platform bed. Works really sweet, very light if I want to move it and while the mattress is a little thin, I've found my back problems have gone away. My wife is really happy with it too. I really advocate that folks with roof tents take the mattress out and use as a guest bed when the tent is not in use, keeps everything fresh. Yes, I know the tents don't leak but it takes about 30 pounds from off the top of the car. I don't ever notice that the box is up there and all I do is put the mattress back in and I'm ready to camp.
Rich