As others have said convert your lights over to LED bulbs and buy a 12 volt fan. Hopefully you have 12 volt jacks already installed in your TT.
Your circuit board in the fridge is going to draw a small amount of 12 volt power even when it is running on propane. Nothing you can do about that.
If you have a built in radio the memory circuit in that will draw a little currant at all times too. Some people add a second cut off switch to the memory wire to the radio to eliminate this .
If you have built in smoke/ carbon monoxide/ propane detectors they draw currant too.
I have 2-12 volt deep cycle golf cart batteries. I run the Television maybe a hour or so day on a small 300 watt power inverter. By eliminating my parasitic loads like the ones above I can go camping for 3 days no problem.
Give up on the microwave idea. It is going to draw so much currant it would be difficult to build a buttery bank big enough to make it work. It can be done but, not easily