I know this answer!!! Finally - my months of experience will come in handy!
A front screen thing (reflectix). That's the answer.
I know you were asking about the heat pumps and wanting to see about the efficiency of that type of heat....but this one mod - i know there's a term for what they are, but this changed the temp of our coach within minutes. We have used this front thermal break several times, but this past weekend it was obvious the difference just that one item made.
First night of camping, we were cold. About high 30's/low 40s outside temp overnight. Couldn't keep the camper comfy. Second night (same temps), we installed this thermal break around the front cab, and within 5 minutes had the camper toasty.
It was weird how well and how fast this worked (and clearly not air tight), but all the other vent covers and window covers were the same from night one to night two. The front cover was the only difference.
Btw - anyone know what this is called? It has to have a name b/c our camper came equipped with built-in velcro tabs to attach one.
Here's the pics
RV insulation mods winter/summer DYI