If I read this right and you or anyone else who has the hitch and can pull the pin then as I suspected you are not following the instructions. I suggest you go back and read them again.
Here is part of the manual "Square the RV base legs with the ribs of the truck bed and then tighten the ½” x 3” draw-down bolt to 40 ft-lb. Next, tighten the two u-bolts to 80 ft-lb. to secure the RV Base to the RV Post. It is very important that the draw-down bolt is tightened BEFORE the U-bolts are tightened. When the RV Base is installed correctly, the RV Post should have a ¼” to 1” gap between the RV Post and the RV Base where the draw-down bolt attaches.(PIC F) Also, YOU SHOULD NOT be able to disengage the latch pin in the wheel well when the base is installed correctly."
Incorrect installation could transfer the load to the bed.