Since gas mileage seems to be a large concern, I believe I would get a high gas mileage vehicle and just switch to tent camping. A tent could give you a lot more room to spread out and be comfortable anyway.
I have my camper van, but when camping with friends, we use tents and have a blast. We have tarps we can string up to cover a large area if it’s raining to keep out entire camp site dry.
It’s a little more set up & tear down, but the expanded space makes for a more enjoyable experience.