I'll chime in re: the 1640 ESP, I have one as well. Been on some pretty rugged trails, pretty happy with it so far. As for cold, I had it out last October for elk season in CO, and it was pretty much single digit temps. The propane heater works well, but within minutes of turning it off you lose all the heat because there is so much square footage of thin tent material. Which is fine, bundle up in the sleeping bags and kick it on in the morning before you crawl out of bed and you have a nice toasty trailer to get dressed in at least. Not sure how much propane I used over the week, I found a small leak from one of the hoses I had to fix mid trip so I'm sure that contributed to using a tank. Other considerations though, with the temps so low the rubber weather strip under the beds lost all pliability and there were some pretty large gaps between the hard trailer and under bed joint. We actually had snow come in one night. So, did it work, yeah. Not sure I'd do it again. That cold at least....
We also had a sealant failure after owning it for less than a season and got some water in around the vent. Forest River told me that it was not under warranty as it is a "yearly maintenance item". OK, I told them, I have not had this trailer for a year yet! So you're telling me a "yearly" maintenance item on a less than one year trailer is NOT under warranty? Yes sir. OK. So, I stripped all that off and used some high quality 3m marine grade sealant. Hopefully that prevents any future issues.
Other than that, it's been fine. Finding the build materials/quality is leaving something to be desired, but I've got the mindset to fix/upgrade stuff as needed. Next project is to upgrade the under seat and cabinet storage to keep things organized and from shaking all over the place.
