For some reason, trailers built in Oregon are better insulated than most. Northwood trailers (Artic Fox, Nash and their 5th wheels), and Outdoors RV are both good choices. But hard to find out east.
If you cannot get thermal (dual-pane) windows as an option, the trailer is probably not really 4 season and well insulated.
EDIT: and yes, we too will probably have to go out West to get one.
2014 ORV Timber Ridge 240RKS,8500#,1250# tongue,44K miles
690W Rooftop + 340W Portable Solar,4 GC2s,215Ah@24V
2016 Ram 2500 4x4 RgCab CTD,2507# payload,10.8 mpgUS tow