Determine the towing capacity of your truck, using your owner's manual or Towing World's Annual Towing Guide. Also measure your truck bed. This is important information to find out so you know how heavy your new camper can be and how lightweight your materials need to be.
Purchase plans for your camper shell from a DIY camper plan supplier. There are several places to find plans of varying sizes, including RQ Riley, Glen-L and Butler Projects. Be sure to purchase plans that will fit your size of truck.
Purchase the materials needed, according to your camper plans. This often includes siding, plywood, paint, hardware, glue and caulk, and windows and doors. Also make sure your tools are in working order--your drill with plenty of torque and your saber saw sharpened for quick cutting.
Build the frame. Your plans will call for you to build your box off the truck bed, assembling a plywood floor, two by four walls and roof joists. If your plans do not specify, be sure to use rust-proof screws to ensure longevity.
Place insulation in between boards of the frame and cover with siding. Depending on the budget for your camper, you may be using simple plywood for the siding, or you may be using more lightweight and more expensive fiberglass or aluminum siding. Whatever you're using, be sure your holes are cut for installing your windows and doors.
Install and seal your windows, top vent and doors. Seal the edges with weatherproofing material.
Install trim on the corners of the camper shell, using aluminum molding or a weatherproof caulk, depending on your budget. Seal any other places that may be susceptible to rain or wind. If you're using plywood for your siding, seal the top with a roofing tar or weathersealing paint.
