we've used a dometic with our 550 for more than three years. I really like this unit. It's proved to be tough and reliable. I keep it at 35-37 degrees.
After killing a battery by discharging it too deeply too often and not frequent enough full charging, I now carry the dometic in the TV. When we get to the campsite it moves to the trailer side table and runs off that battery until we depart. I have found that this allows me to get to the campsite with a mostly-charged battery. This is important, particularly in warm/hot weather.
We also carry an 85 watt solar panel (sized to fit in the TV) and if we can get even a couple of hours per day of decent sun it really extends battery life with the dometic running. I find a way to fully charge the battery at least every five days, and have never discharged the battery below 60%, according to the trimetric monitor (a great addition if you want to do much dry camping).
We also have the insulated cover on the dometic. Even if we stop for an hour or so I find that the temp rarely goes up more than a degree or two. The dometic also restarts automatically when the TV is cranked up. This is great because I'm sure I'd forget to turn it back on.
One more thing - if you use a portable solar panel and a decent length cord (ours is 30 ft), you should definitely have the Sun Seeker app. This will show you the path of the sun at your location so you can optimize the placement of your panel. It works with the gps so it doesn't need any internet connection.
hope this helps.
R Dickson
550 #645, 165 nights and we'll break 40,000 miles this Sunday