Keeping Warm in an R-pod

Small ceramic heater will do you just fine down into the teens. Open the FF vent just a half inch, and one window an 1/8th of an inch to prevent humidity issues. 

Yeah 38 is nothing... Camp in the Rockies in the summer and it gets colder than that....

We tried a vent cushion. I returned it because there wasn't enough depth to hold the cushion in place. OTOH, the reflectix in the windows is a great idea since the R-Pod's windows are single-pane. It will help. Also, they will work better than the stock blinds for cutting the light, making it easier to sleep.

Both an electric heater and the R-Pod's furnace do not contribute to humidity. However, we contribute with perspiration and breathing and activities like cooking also contribute. Having the vent and a window slightly open will help remove the excess humidity. Otherwise, you will find condensation dripping down your windows and your mattress and bedding will get quite damp. If you use a Mr. Heater Buddy or catalytic heater, these really contribute moisture as they turn propane into CO2 and H2O. Venting is needed for both ensuring you don't poison yourself with CO2 or turn your R-Pod into a giant sopping sponge.

Well I have been down to 5F in my 179 with an electric heater and some supplemental heat from the propane furnace.   I think the propane could do that low of a temperature on its own.  I all ways leave the bathroom ceiling vent open a little bit to control condensation.   You can close the window blinds to cover the windows and help with insulation over the single pane windows. 

I like your hydronic heater. Where did you get your heater core, pump, and fan? Where did you place the pump? Did you connect it in to the thermostat somehow? With this, do you still use the furnace or is it only being used as a cold air return?