Insulation is certainly a personal preference. I have been in my bus for over a year - but travel with the weather (for the most part).
Right now, it's 20 degrees out - with temperature ranges from 32 to 12 degrees.
I wish that I had better insulated the floor - but the walls and ceiling are factory insulation - which was in good shape for a 18 year old bus.
It is easy to keep the bus at a decent temperature for me when plugged in to shore power - I have two small $15 heaters that work great - but it's about 55 degrees at night when the temps drop below freezing. it is a little drafty near the doors and windows - but I cover the windows by the bed - and sleep soundly.
I have a propane Mr. Buddy Heater that will heat the bus in minutes and take the chill off.
My cubic mini wood stove really warms up the bus nicely - though it does not last through the night.
Last Night was chilly - but the wood stove burned from about 6pm to 11pm.
This morning the temperate in the bus was about 53 degrees (outside was 16) with the two electric heaters running all night on low. A few minutes after lighting up the wood stove it was very comfortable.
As I mentioned, I wish I would have better insulate my floor and doorway - other than that, I am comfortable as it came. In the summer - I can open the windows and run fans - it has rarely been uncomfortable - if it gets too hot out - and I am in direct sun, I use Reflectix on the outside of the windows in direct sun - and that makes all the difference.
Without AC - it is generally only a few degrees cooler than outside - or about the same - unless I am in the shade - but a small portable AC unit will help - the windows seem to be the biggest summer heater and winter cooler for my bus.
One day, I hope to get awnings to help in the summer. For now - Reflectix on the outside of windows in the summer sun - and inside of the some of the windows for cold winter nights.