We have a class B van camper, mostly because of health issues that necessitate having a bathroom with us when we travel. Nothing about it is frugal, per se, but we do our best to make it a bit more mustachian. We are a family of four adults (although the almost 20 year old has delayed getting his driver's license because paying for auto insurance when he would rarely get to drive doesn't make much financial sense). Three adult drivers share one subcompact hatchback, and the Sprinter van camper. We rarely have to use it as the second vehicle, but it is there. We also use it to carry things if the cargo space in the car isn't sufficient. We use it as a bike race support vehicle (place to change, to shower, to hang out in, and to bring our own food). It's nice for day trips -- we can carry food in the refrigerator and cook in the van, shower off the sand from the beach, etc. With careful driving, we typically get 21mpg, which is better than the Tacoma truck we used to own.
For camping, when possible we either boondock or "stealth" camp in it, avoiding camping fees. BLM dispersed camping is free, as is staying in a friend's driveway. We'e figured out how to sleep all of us in it reasonably comfortably, although it's much better with just two of us. When we travel, we make a point of taking all the food we will eat and cooking in the van, versus having an eat out mentality, even in cities.
We did used to have a fiberglass "egg" style camper, but stopping every 20-30 minutes to get to the bathroom wasn't tenable. We bought it used (bought a 2009 Escape in 2012) and sold it in 2015 for the same price we paid. Of all travel trailers, I've never seen anything hold value as well as the fiberglass egg trailers. It's amazing to see someone asking $10K for a 25 year old trailer, but they get it. Maintenance on the fiberglass trailer was super minimal, mostly just repacking wheel bearings each year. The van has more expensive maintenance by far.
Without a doubt, the van camper is a luxury item, but it's paid for and we're good shape finanically. We aren't FIRE, in part because we want to assist our boys with their schooling, but mostly because DH doesn't want to leave work yet. Still, if his job was gone tomorrow we could work it out without him going back to work, and I already don't work for pay. Even assuming we live to 100, have to finish paying off the mortgage (only debt), and never receive a penny from social security, FIREcalc shows us with 100% success. (We would have to use SEPP and participate in ACA.) So I don't let myself feel guilty about the camper van.