Window Air Conditioner Foam @ Home Depot
OR
Garage Door Bottom Seal @ Home Depot
And
Outdoor Mounting Tape @ Home Depot
I've personally used the tape on a freshly painted front bumper (my VX) and when I removed it the paint was un-harmed.
I would shy away from using a tape running the gap between the bed and cab as the two will move independently of each other do to frame flex. This will cause the tape to distort and possibly tear.