You see all those nice Camper vans in U.S.A & Europe? Remember, they have very cold weather sometimes and need to do many things inside the vehicle like Cook, Wash & Dine.
Here in Malaysia the weather is mostly HOT! Use your Van for sleeping and Storage of your gear (Plastic Boxes work well). Take it all outside! Get a Tarp or a 10'x10' (or x15') fold out Canopy (Pasar Malam Type), My Bed platform converts to a Table (Banquet table legs) out doors or just get a banquet table at Tesco. Buy a Toilet Tent & a Porta Pottie. The little Butane gas Burners ( Not the tiny backpacker one, home one with cartridge.) are cheap and work fine, Poly carbonate water Jug for drinking water other jugs for wash up water. These local camper mods just clutter up the van, block windows, loose lots of space and cost allot. Cooking in the Van smells up the whole place (oil residue, maybe curry/salted fish?) and can be dangerous!
If you want to put back seats or haul gear or anything it's still possible. Don't forget JPJ & Puspacom can make your life miserable with any mods. Maybe a platform for a bed that converts into a table is good as you can also hide gear underneath out of sight. Keep it simple, see how your uses turn out ( I use more for Picnic/Day Trips than actual camping these days.) and go from there for any mods. My van becomes my Living Room & Bedroom while the outdoors is my Kitchen, Dinning, wash up and toilet.