I've got a Small Truck Skamper Camper the roof interior is totally saturated w/water. Any ideas on how to repair this would be helpful. Considering tearing the interior out and replacing w/something.

You'll want to stop the water infiltration from the outside so adding a EPDM layer might work. You probably want to remove & replace the inside materials 7 insulation as wekll to get rid of any mold problems. Hopefully water or mold has not started creeping down into the walls yet.