I have a
Scamp 13' with no built-in heater and I also use the combo of a small ceramic cube heater when plugged in, and a Coleman Sportcat catalytic heater (similar to Blackcat) when off the grid. However, I don't feel comfortable letting the catalytic run all night while sleeping (it is rated as safe for inside use, but makes me nervous). Instead to save on fuel, I use a hiking Nalgene water bottle filled with hot water in the foot of the bed. I made a little fleece drawstring bag for it so it is nice and soft. Toasty.