I thought it might be time to post some info on my external air conditioner setup. We bought our Scamp
13 last fall
and along with it came a new GE 5,000 BTU window air conditioner. The previous owners had built a shelf/bracket to mount it in the rear window as others have done. My wife and I didn't really want it up there right over the bed, so I investigated several othe options, most of which required cutting holes in fiberglass. Both here and on the Teardrops and Tiny Travel Trailers websites I saw postings about ground mounting the air conditioner and piping in the air, so that's what I settled on. I built an enclosure for the AC unit which essentially protects the part that would normally be inside the window, and provided a bulkhead to seperate the cold air output and warmer air return. The only mods to the AC unit itself were to drill a drain hole in the rear corner so I could be sure it is dumped out before repacking, and to reroute the power cord so it exits the rear of the machine instead of the front. I'm not sure I'd bother with this again. Definitely want the drain hole, though. The pictures should be pretty self-explanatory. All materials came from Lowes, except for butyl caulking that I put around the AC unit in the wooden enclosure, and some sticky stuff in a tube (one of the favored products on this site) that I used around the metal ducts to seal out the rain. After the machine itself is inserted into the box, I installed a metal strip across the back to keep it from sliding back out. All duct work is six-inch, which I would consider a minimum to reduce pressure losses. Lowes sells a six-inch flex hose which works great. Ideally, I'd have a larger return line (8" or so), since it's operating at lower pressure than the cold one being pumped toward the camper, which would come closer to matching the area of the AC intake. For this reason, and so I could bleed in some fresh air if desired, I added a fresh air intake on the front (a small register unit). The return line connection on the side of the box is removable for travel. I made a bridle out of safety wire that I hook to a spring across the front to hold it in place. This one is obviously not caulked in, but I don't really think that's an issue. I put a small drain hole in the front floor of the box just in case, though. Weather-proof wise, I tried to do everything so that water would have to go uphill to get in. Obviously, if we have a flood, there will be problems. I may end up making a slightly elevated mount of some sort.
So how does it work? On a recent trip to Asheville NC, it got into the 80s with high humidity, so we hooked it up. In no time, the trailer was much cooler and less humid. When we got back to Ohio, it was hotter, so I set it up in the driveway in 90+ degree direct sun and high humidity. Within a short time, the trailer was in the upper 70s. So far, all controls are original. Setup and teardown is easy. The warm air return connection at the top of the trailer is held in place by the vent lid. To install, all I have to do is lay the thing up there, then reach through the vent/escape hatch and put it in place. The cool air connects into an adaptor made from masonite that fits in the weather stripping in the back window. I "hinged" it in the middle with duct tape to make it easier to install and remove.
What would I do differently next time? I've thought about installing a 24V transformer to power a thermostat in the trailer that would switch the compressor on and off. (Both nights in NC, I had to go outside to turn off the AC.) Rather than go through the thermostat mod just yet, I'm going to mount a box on the panel that sits in the rear window that will allow me to turn the entire unit on and off. Essentially an extension cord with a switch in the middle of it. Next time, I'd be more careful with the fins on the back of the unit and maybe install an expanded metal grill across them. It already had some areas where fins are bent, and I added a few of my own. I've made a panel to put in place for travel at least. We need a deflector to send the air up a little higher when sleeping. We sleep with our heads at that end of the bed, so a little angle plate of some sort should solve that problem. This will be removable, though, so we're not sending cool air straight up to the return line in the daytime. Ultimately, I may connect the cool air line into some sort of register in the floor beneath the bed/dinette, which wuold probably make the air flow more uniform. What I have now with the masonite flange in the rear window was quick and dirty, but it's simple and works.
Okay, enough words. Here are some photos.