Get a light from a junk yard (allhyundaiisuzu - don't know the web site) and wire it into your existing dome light. If you use a snake (or coat hanger) to fish the wires, you can hook it right into the existing wiring there. When you open the doors, it will come on with the original, or you can push it on. If you want it to work with the back door, wire in a pin switch to the back door as well. This will activate all your lights when the back door is open.
"If you're not living on the edge --- you're taking up too much space!!"