Ray, you should have a little baffle-door just inside the microwave vent, up high on the outside of that slide. That little door opens when the microwave fan is turned on, and it's supposed to close under its own weight when the fan is off. Is there any chance it's stuck in the open position? That vent is right over those cabinets and if rain got inside, it might drain down behind those cabinets.
My outside TV is also under that vent. Have you checked the rubber seals on that door? It looks like there might be a path to those cabinets if water got in there, although I don't think it's real likely.
Kev
By the way, you can inspect the upper slide seal (sort of) by standing on a ladder at one end of the slide (when the slide is open) and use a flashlight to look under the slide topper at the seal. You can inspect it from the inside by bringing the slide in about half way, then stand on something by the passenger seat and look over the top of the slide.
Kev,
My vent is closed on the microwave we don't cook inside we use an outside stove. I haven't checked the outside TV but will this morning. That's a good ideal on inspecting the seal I will try that. Do you think it could be plumbing? Thanks