trailer (1 of 2) That is what happened to mine, looked just like yours and its a KZ Coyote. The tape in the pic is covering the gap temporarily.
Mine is certainly due to water infiltration. Water could get in between the top of the bunk door frame and siding. The D seal was also in poor shape and the door didn't seal properly at the top area. With the wood damaged beneath the laminate, not much for the screws to "bite" into.
I believe the water infiltration has been fixed by recaulking and new seal, but the wood inside still needs to be fixed.