Decide if you want a vehicle with its own driver compartment or one that will be towed by another vehicle. For a driven camper, a small bus or large van will do the trick. For a towed vehicle, look for an appropriately sized storage trailer---one designed to carry something like a car.
Take out any rear seats that are in the vehicle. For a van, you should cover the floor holes the seats leave with more carpeting. On a bus, a couple of seats may be left if they can work with any of the "rooms" you create for the camper.
Cut out windows in the trailer for circulation. This may involve flame-cutting tools, depending on how thick the trailer siding is. You could purchase an RV window kit, cut the holes to fit the windows and install them, or you can simply hang curtains over the cutout windows from the inside.
Place a bed inside the vehicle. A good trailer location may be in one of the rear corners, while up against the front seats is good for the van. This can be a fully constructed bed frame secured to the floor with a mattress, or it can be stacked foam cushions with a sleeping bag on top.
Construct the kitchen. Attach a table to one wall, add side panels to the legs, put a camping stove on the table and secure a toaster oven, microwave and the stove's propane tank under the table. This area must be near the rear opening to allow ventilation for the stove.
Complete the kitchen with a sink. Cut a hole in a smaller table, fit a stainless-steel bowl in the hole, and install the table next to the kitchen. Keep jugs of water under the table to pour into the sink bowl, and make sure you can remove the bowl easily for water disposal.
Build a dining area near the kitchen if you have enough room. Secure another table to the wall and then secure chairs next to the table on the floor. You could use any of the seats that came with the vehicle, especially if it's a bus.
Find room for an entertainment center. Install a set of cabinets on the wall that that can store a TV, DVD player, game console, stereo and other devices.
Install lighting (if it needs it) by storing multiple lamps inside. Secure them while moving the vehicle.
Stock the camper with power supplies for devices like the ovens, TV and lights. Get three or four deep-cycle batteries along with power inverters. Install insulated boxes that will store the batteries and allow access to the plug sockets for the inverters they are connected to.
