Just keep in mind that the
working amp hours available is only 50% of the rated amp hours (AH). That means that you have a maximum of 40AH available from a fully charged (brand new) battery. That constantly changes with age.... Just like us...
That means if you have 3, original light bulbs in your camper that are rated at 1.7A each, you can run those 3 bulbs (total of 5.1 amps) for 7.8 hours (5.1A bulbs for 7.8 hours = 40AH (amp hours).... total useable capacity of the battery.
Throw in water pump usage, ceiling fan and whatever else and you're done until the battery is recharged. The trick is though (as I said before) if you only charge that battery for an hour, you've only put about 12AH back in the battery and it will be dead again with about 2.35 hours of those 3 bulbs (instead of 5.1hrs).
When your battery is fully discharged, you would have to plug your trailer into house current or your battery for 4+ hours to about 90% charge. (the calculation gets a little fuzzy because you have to allow for absorption and other things).
If you intend to do much boondocking (real camping) you may want to think about adding solar. 1, 100w solar panel would work nicely with that battery and probably keep you fully charged with what you can use. a 100W panel will give you about 45AH of charging (your battery's capacity) each day (depending on amount of direct Sunshine). No matter what, it would do better than running your generator for an hour a day.