Microwave Vent Damper

Hello
I have a question regarding a microwave vent damper. My last trip I noticed that I was drawing in moisture through my microwave and it was dripping condensation on the counter. The cause was from the temperature difference between the inside and the outside air temp (microwave not running). Since then I pulled down the microwave to find that there is no damper on  the microwave or in the roof vent for it. On my 2552 the microwave vents to the  outside via a roof mounted vent. I believe some PC's vent inside, when there microwaves are located in a slide. Anyhow have any of you installed a vent damper or had moisture issues with the microwave from condensation?

I am going to purchase a microwave vent damper and install it in the roof opening, my only concern is that it will flap around and make noise while driving down the road.

Another issue is that the vent is directly open to the outside air, meaning there is a free exchange of air between the inside and outside of the PC. This just causes another heat source that you have to overcome in the dead of summer.

If you look at the lower picture you can see that the roof opening doesn't line-up with microwave fan, they are offset.

That's actually a refrigerator exhaust vent that PC uses.  I believe it would be much better to make a gasket to seal the top of the microwave to the ceiling opening using soft rubber or closed cell foam.  I say that because yes, a damper has to be light enough to easily open so will probably flap A LOT while driving.

That is my concern as well that it will want to flap around. I already ordered the damper so i might as well give it a try. If it doesn't work then I will close off the opening and make the microwave vent inside the coach.

Without a damper of some sort, there is a lot of heat loss when it's cold outside.  The microwave oven might also develop a serious amount of frost on it from the humidity inside the house.  The top of the microwave in EngineerIt's pictures does seem to have some sort of dark gray rubberized insulation adhered on it.

I never realized that the current-day oven/hood combo unit vented through the roof instead of through the side like our older stove hood has.  The oven/hood today makes one more hole in the roof.    I suppose a side discharge can't be done because of the awning being in the way.

Another odd thing about EngineerIt's pictures.......Based on the cut-out in the microwave backing plate for a side discharge, the roof vent is far out of alignment with the top-discharge.  That does not look right at all.  I wonder if a ceiling joist prevents Phoenix from properly aligning it.

Does the exhaust from the microwave oven just swirl around above the microwave before finding it's way out the roof vent?  If so, that would mean all the surfaces would get greasy.

Going from the earlier stove hood with separate microwave to the current day method, has some issues I never realized until now.

It looks to me the left vent outlet on the microwave is blocked by a plastic insert thus the right vent blows directly up through the roof exhaust area.

On my 2551, on cold days where the coach is closed up but the bathroom vent is on, that I can feel cold air coming in between the right side of the microwave and partition wall between the kitchen and bedroom area. 

It does not bother me enough to try to seal up the top of the microwave but it is open to the exhaust cover.