I don't know what disconnecting the negative pole and leaving the positive connected might implicate, but there may be other negative connections somewhere. Newer trailers have little power draws even with the battery disconnect switch in the off or disconnected position. Such little things as the CO2 detector, digital clocks and other little gizmos that use 12v current. In most situation it won't kill the battery, but a weaker battery or extremely cold weather can cause it to draw down over the winter. Happened to me with a brand new trailer in storage. Removing the battery when the trailer is in storage or keeping it on shore power, if available, or a solar charger, would likely prevent this from happening. I agree with the suggestions about getting the battery checked and/or charged by an auto parts place. BTW, all the dealerships I've visited in cold weather fully remove the batteries and keep them in doors when the units are winterized.
Former: 2007 Cardinal 30W LE
Now:2018 Arctic Fox 27-5L
2008 Ford F-250 Long Bed Diesel
Total of 30 Months on the Road Since 2008