When we were looking at used fifth wheels, we noted wet and rotting wood in several places. So when we found one that was in good shape, we made some modifications.
First, an aftermarket trim piece across the top of all the hatches to divert the water. These pieces come in various lengths, and we painted it white.
Plus a metal strip across the bottom of the hatch for the fridge so any water that does trickle into the bottom edge can't go into the hatch.
I noted a wet area on our camper this fall; water had collected around where the jack attaches to the camper. When I pulled the lower edge trim back, there was water collected along the inside of the trim. That took some butyl tape and silicone-type stuff to seal off well.
