UPDATE: So I figured out how to get to the converter the other day. It's mounted vertically in the basement behind a carpet covered panel. I removed the screws holding it in place so I could confirm the brand and model number, and get a look at the back side where the DIP switch for selecting the battery type is, as ChuckS suggested. The switch was set correctly so I remounted the converter and put the cover panel back in place. The strange thing is now it seems to be working correctly; I left the trailer plugged in for a couple days and my volt meter showed a constant 13.7 volts the entire time, the battery didn't drain at all. I unplugged it earlier today, and the volt meter has shown 12.9 volts for several hours. I also noticed that the cooling fan hardly runs at all now, previously it ran almost constantly, even when the trailer wasn't plugged in to AC and the converter should be inactive.
I didn't change anything, just removed it from the wall so I could get a better look, then put it back. So it would appear that just jostling it around has fixed (at least temporarily) whatever problem it was having. Does that make any sense?
