Solar Panel to keep battery charged while away...

Wll your trailer is newer like mine and based on my experience having the trailer just sitting there using propane and running the fridge and parastic loads is going to be about an amp/hour or 24AH per day (its higher than you think)

To replace 24AH/day I wouldn't go with anything less than 100W solar which is typcially good for 30 to 40 AH/day. I would also upgrade to twin 6volts in addition to solar so that if you have a couple cloudy days you have enough capacity to maintain.