I don't know the R-Value of our A128s. I do know that it gets mighty drafty around the "cool cat". I love it when we can use the heat pump. The heating is more uniform and not so harsh. Unfortunately, with a 40 degree ambient temperature cut off it doesn't get as much use as I would like.
The propane furnace alternates between toasty to too cold to I am getting cooked! We have never found a good setting for it except when we set it extremely low and cycle it as little as possible. The thermostat (digital) seems to allow too wide of a temperature range. (The furnaces works good for dry camping except that it will eat up your battery life.).
We've camped for over 90 nights in our camper (quite a few of those nights were in cooler weather). We cook, heat, and always have the water heater on. We have used around 4 tanks of propane.
Our small electric heater is almost adequate. I may try to buy a larger one in the near future.
We camped through this weekend (Thanksgiving). 2 of the nights got down into the mid 20's. Besides the many periods of wide range temperature fluctuations, the camping was great!