Removing our rear A/C unit.... to install solar panels

14" sq box from plywood
insert from inside the rv to flush with roof
fasten fro the inside with screws into the frame members
on top, seal edges with enternabond overlapped onto the roof
paint the plywood with rubber roof coat, several coats
cover the whole thing with a two foot sq of rubber roof material EPDM or TPO

or you could just install a standard roof vent
and mount panels high enough that they go over the vent