[TIDALWAVE]

While washing my JL Rubi, I discovered that Jeep decided to save a couple of bucks by not sealing up the access gaps in the sheet metal where the tail hinge brackets extend into the tub. If you swing open the tailgate, you can just about insert three or four fingers into the gap next to the hinge brackets.
You are going to get a lot of dust/sand going into the body cavity. Even worse, salt water if you live in a colder climate where they salt the roads.
I have tried to make a couple of rubber gaskets to glue around the hinge brackets to seal the gaps (1/2 inch x 2+ inches).
You might be able to use some closed cell foam and squeeze it into the gaps to help seal them.

There is an expandable water proof spray foam I may use next if the home made gaskets don't work out.

 

[Comanche]

Would love to see a picture of your solution if you end up addressing this issue. A bit disappointed to hear that FCA continues to cut corners like this, but hopefully its something that can be DIY fixed.

 

[Goliath]

You could also look into hydrophobic spray, which should prevent too much grime from accumulating on the hinges. Rugged Ridge has had some better aftermarket hinges/tire carries on the JK.