I have a old 4x4 SUV converted to a camper van.
I know people with full blown camper van conversions, mostly built on the back of pickups. There are lots of Thailand camper conversions on YouTube. Aircon is the killer... finding places with an electric hookup suitable is not easy.
Thailand has some wonderful national parks that offer camping. There are plenty of good campsites too... some where you can literally park up on the beach. Most have toilets and showers. We've never been refused because we have a van, not a tent.
The SUV suits us. Most of our time (including cooking and eating etc) is outside under the awning, so we only need somewhere to sleep. The van has a decent solar setup, sufficient to run a fridge and large fan overnight.
A camper conversion based on a minivan would be more comfortable. Although it would have been more expensive, initially, I did plan to go down that route. However, Thailand has so many cheap hotel and guest houses, it just wasn't worth it.