Now that it's getting colder I've been running it 24/7 on the low fan speed plus some low wattage electric heaters and it's kept the humidity around the 35 - 45% range, so nice and dry in here, even with the roof vents mostly closed. Not getting any condensation on the walls or windows so quite happy.
You are different though as you aren't living in the rig. We are constantly putting moisture into the RV with our breathing, showers, cooking, etc. Unless you have a water leak there shouldn't be much moisture inside to worry about.
I don't think you should have a problem, just leave a roof vent or two open a little so you can get some air exchange. Also, a good idea to open up all the cupboards and pull the mattress away from the wall.
For us the humidifier pumps out a ton of water, the 19-pint tray was filling twice a day before I put the drain hose outside. But I imagine a trailer in storage will generate much less.