We live in Arizona where we RV year round.
In the Summer the weather is daytime 70-85, 40-55 nights. A/C easily kept it nice inside. At night we used the heater just enough to take the chill out. I prefer it somewhat cold with lots of blankets. The propane furnace works well but does need shore power or the battery runs out quick running the fan.
On colder nights that dropped into the 30's and low 40's we used a ceramic heater sitting on the counter in the middle of trailer. It easily warmed the entire trailer up.
We also used solar blankets from popupgizmos over the bed ends. This helped keep the trailer nice cold or hot considerably. When we traded our Starcraft 21SSO for our current trailer I forgot to include the solar blankets. Still have them in our garage if anyone can use them!