Yes, moisture will be your worst problem. RVs are built backwards from houses in that the impervious (vapor retarder/barrier) is the outside skin & roof. Moisture will migrate through the interior luan walls and ceiling and condense against the outer skin/roof. You may not see anything but over time can cause rot & mold. In the worst cases of daily use over the winter without removing moisture, water can drop from the ceiling like rain and appear to be a roof leak...
In the early and late season when temps around here are a few degrees (F) above freezing, it can take maybe an hour or more before it feels comfortably warm inside. An RV has thermal mass which you will need to overcome somewhat and takes time. Temps. down to 20F will obviously take longer.
If you have a heated underbelly, a LOT of heat will be going straight to the outdoors. For winter use, perhaps you could consider blocking off the furnace ducts into the floor cavity.
I have a feeling that a dehumidifier alone won't help enough as there will be a sudden moisture buildup when everyone walks in and takes off damp clothing and if you do any cooking. You may need a dehumidifier and need to crack some vents also. A hygrometer to measure RH might be a good idea. You'll need power for a dehumidifier tho.
I installed permanent recessed electric heaters in our TT (1750 watts total) and don't use the furnace anymore. You could do something similar or have a couple of oil-filled heaters and put them on a 7 day/24 hour time switch so that say, every weekend at a preset time, you bring the interior up to a min. temp of around 15C. Then use the furnace to bring it up to a warmer temp if desired. If no permanent power available, not an option.