There are a number of parasitic drains on the battery, even with the disconnect in the "off" position. The LP leak detector is one (for safety reasons it is direct wired to the battery) and another, if you have a stereo unit, is the the unit itself. When you pull the disconnect, go inside the trailer and look at the unit (most likely a Jensen) and the faceplate is probably still illuminated. It, too, is usually direct wired to a battery feed so that the clock stays up to-date, but, there are other functions beside the clock in the unit that draws power. Even the break-away brake switch will leak a little current over time as it gets wet in the rain and the rain water creates a small current path to the frame. It all adds up over time and can drain a battery fairly quickly.
Most trailers are built that way. If you haven't installed your own disconnect switch directly between the hot wire and the battery, then the only "true" disconnect is going to be disconnecting the hot wire at the battery. Those of us that are fortunate enough to be able to have an RV electrical connection at our storage area (in my case at my house) just leave the trailer plugged in 24/7 without worrying about it. I put in a 30 amp RV plug for my trailer and it powers the trailer all the time; I can fire up everything in it except the 2nd A/C unit prior to a trip or in the off season if I need to vacuum the carpets or "pre-cool" the refrigerator. I've even used it as a guest apartment for visitors if I run out of room in the main house. If you keep your trailer at your house, you could get a 30 amp to 20 amp dogbone to allow you to plug it into a regular household socket and you could just leave it plugged in all the time or you could install a dedicated RV 30 amp plug. If you store your trailer at a storage facility, then your best bet is to disconnect the hot cable (black on most) to remove all the loads from the battery.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)