I'm a little further north than you are
and here is what I have done: one year I used compressed air to blow out all the water. Another year and this year I have pumped antifreeze through the pipes.
Mine did not have a water heater bypass system, so I installed one at the price of some skinned knuckles. I now have three little valves to turn and a clear plastic pipe hanging there ready to be dipped into the antifreeze bottle. I find this just a little easier to do, and if you unexpectedly get into a hard freeze overnight while camping (as I did) it is quick to do, most of the process takes place inside the trailer where it is warm, no compressor is necessary, and one person can do it quickly.
When the Burro
is stored in the back yard I leave it plugged in (guest house). Some years ago I installed a little electric heater permanently in the wall and connected it to a conventional digital thermostat (with a relay). I leave it set at 45 degrees. The wattage on this unit is variable from 250 watts to 1500, and the fan is so quiet nobody notices. I leave the little kitchen window cracked and the overhead vent likewise and have never had any problem with mold, excessive humidity, etc. I think the slightly higher temperature inside is enough to lower the relative humidity enough to avoid problems. An additional point: our refrigerator
does not have a drain but empties into a plastic condensate pan under the fins. Before I realized this I routinely did not check it, so moisture was available for mold inside the frig. I now empty and dry off this pan after every camping trip and leave the frig door cracked when in storage. Problem solved.
You will probably have to adjust your remedies since you are further south than we are.