OP here.
Some of you really should read the original post before commenting.
This trailer does not have any parasitic loads. No tv, radio, etc. No monitors, alarms, detectors, etc. There are no circuit boards for the water heater or the fridge.
This is a 1975 trailer. Most of that stuff wasn't around back then, and I have not installed any of that into it. It is sitting about 30km in the bush with no shore power. The battery is only used to power a few lights. The old battery I had, when new lasted the summer before I had to charge it. This one, after 1 night is dead. I have done nothing different to the trailer since replacing a 4 year old battery.
Next time I am out there, I will locate the fuse box and start pulling fuses to see if there is a draw. However, unless it is a short, there is nothing in it that could be drawing power.