Some of this will depend on where you're storing the trailer. From my experience this is what I did. I never left the vents or windows open. If by mistake one was left open I came back to a rig that was full of dirt and little bitty bugs. What I did do was leave the stove vent unlocked so if the rig did developed pressure it had a way to vent out.
I filled the toilet up to the very top with water and placed plastic wrap over it. When I used vegetable oil I came back to a gooey mess. In the sink drains I did use vegetable oil, making sure I did not spill any around the drain, but directly into it. Again to avoid the gooey mess.
Covered the tires, used aluminum foil over the outside furnace ports (to keep bugs out.) I should also have put a cover on the AC unit, but never did. Leave the fridge open, and drained all the water out of the system.
On edit:
I see you have FL in your sig. I also was in a humid location so I placed some trays of non clumping cat litter out, three big tubs of damp rid, and a couple of trays of charcoal. Trays (dish pans really) came from the dollar store and got thrown out in the fall with the Damp rid. Placed crumbled up newspaper in cabinets (humidity again.) I also used Borax in out of the way places, mostly on the floor under drawers. The Borax was in case cockroaches found the rig. Just because yours doesn't have them, doesn't mean the one park next to you is free of them.
The best thing is to ask the local people what they do for that location.
