Very Helpful Bill,
I use my 25 Safari to hunt in the fall in Colorado and camp off the grid in temps down to the low teens in my 2004 25 foot Safari.
I have some of the modifications on my trailer that you suggest such as the Olympian heater and solar charger. Like you, we don't use the Olympian heater while sleeping but it keeps the trailer comfortable without electricity when we are awake.
I suggest a few other modifications. I have upgraded to group 27 batteries from group 24. These fit in the stock battery box if you drill out the rivets on lid. You can re rivet after the batteries are installed. The bigger batteries give you quite a bit more battery power to run the furnace all night.
Batteries won't last long with the stock single stage converter charger. I have upgraded to a three state unit which doubles battery life.
I also have a 2000 EU Honda generator. I have only one solar panel on my trailer and a little extra from the generator is necessary to keep my batteries charged particularly on cloudy rainy, snowy days.
We keep our heat on the low setting at night which keeps the temperature about 50 in the back bedroom. We sleep in sleeping backs rather than make up the bed.
On my wish list are l.e.d. lights. The incandescent bulbs take quite a bit of electricity.
Also the next time I change batteries, I will probably use agms and go with 4 batteries. I remodeled my Airstream to take out the couch and put in a dinette and I have a bit if room inside in the front of my trailer for two more batteries. The agms have more charge discharge cycles and are worth it if you do a lot of dry camping.