There's really no such thing as a 4 season RV. (Not sure about "park models," but I don't think there are any Signature Ultralite park models.)
If you're only going to be in mid to upper 20's and only at night, you can make it work with tank heaters and heated water hose. If you have electric service, use a space heater with furnace for backup. If no electric, you'll probably need a generator, because the furnace fan will kill your battery in a night or two.
Others will have other suggestions.
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10