Follow-Up post:
The window AC performance hasn't been great for any days when the temperature has been above 90 degrees. Even with the large fan on the floor the trailer gets very warm and the humidity stays high. A few days in late spring the temp was 94 to 96 and the trailer was in the low 80's. I then decided to remove the window AC and install a roof AC.
For the roof AC I had to make a few decisions. First, where to put it. Second, which unit. Third, how to install it.
1. Where to put it: The easy spot would be in place of the rear fan, since most roof AC units fit into the standard 14x14 fan opening. However I didn't want to give up the fan. The fan works great for the majority of the time when we are camping. Plus the trailer doesn't have much roof length behind the fan.
The next location is the roof hatch. The hatch opening is 21-3/8" square. This means patching it in but also reinforcing it and making the roof thicker. Roof AC units have a minimum thickness. The roof's
fiberglass is a bit over 1/4" thick. AC's usually need a minimum of 1.5".
2. Now that I had picked the install location, next up is which unit. I looked at installing a Dometic Penguin 2, but it had some downsides.
Weight is about 120 lbs and its a bit wide (I plan to install
solar along the sides of the roof). I heard good things about Rec-Pro's Houghton AC units so I researched them. Benefits are
weight at 67lbs, lower width, and very quiet when running. So that was my pick.
3. Last is how to install it. I removed the old hatch and sanded off the gel coat down to the
fiberglass where i'd be attaching a new frame. The roof needed to be reinforced and also made thicker. So I made a small wooden frame and attached it to the fiberglass using marine adhesive. Then i attached a piece of 3/4" marine grade plywood to the top, fiberglassed over it and onto the trailer roof, and lastly used gel coat. This made the roof extremely strong (easily supporting the
weight of myself and my brother). The gel coat isn't smooth, but since you'll never see it I wasn't worried. And, it will be covered up by
solar panels anyway.
I then measured where to cut the 14" hole and made sure it was centered in the existing opening from the inside. The Houghton's interior vent & return air grill is nearly the same size as the old hatch. I only needed to trim it out at the corners. I used some white PVC sheet that I had on hand. (I'm not totally convinced with how it looks. I may switch it out for birch plywood to match the rest of the trailer)
Finally, I removed the window AC under the seat and filled in the hole with finished plywood (no photo currently)
Performance: Yesterday at noon it was about 96 to 97 by afternoon with 54% humidity. The inside of the trailer started at 89 degrees and within 45 minutes it was down to 80 and 26% humidity (felt noticeably cooler due to the low humidity) By 1hr 30min it was 76 and 27% humidity. 2hrs it was 74 degrees.
Later in the late afternoon & evening when the outside temperature was 90 the inside of the trailer was in the mid 60's and it felt cold.
If the weather here ever reaches 100 or higher i'll retest things and post how the performance is.
So far this has made a huge improvement with how the interior of the trailer feels.