I've left the empty camper outside for a few days to see how it handles the rain.  Although it's painted outside I've decided to keep the inside natural.  The camper was closed however it soaked a lot of water to the point where the joints on the bottom got saturated and swelled.  If there were any belongings inside, they would be soaked.  Due to this I believe this design has a flaw.  To remedy the problem I would mount the wheels on the sides where the latch for the lock is located.  This would require you to flip the box 180 degrees when in the transport mode.  However this would make the top board solid without any holes and be a much better protection from rain.

I have also started working on a new version of the camper which will eliminate the crack between the two halves.  Here is an 4x8 ft plywood cutting pattern with sizes in inches.

 AF and BF edges have hinges.  Hinge design also needs to be addressed.  Waterproof hinge  can be made of strong fabric strip covering full length of the joint.  This would solve the problem with water getting in, however it creates a new problem where the hinges can be cut with a  knife breaching the security of the box.  C and D are mounted to the sides of A and E.  This way F and B will also fold in-between  C and D to make a water resistant joint.  Coaster wheels will mount on side C or D.  New tarp cutting pattern for  the tent is needed.