I am sure someone else with motorhome experience will be along shortly but what battery is dead?
Starter battery or the house battery? Both?
All trailers and MH have parasitic draw that will kill batteries if they sit for too long. The propane and CO detectors are the usual culprits.
If you don't have the means of plugging in the MH while it is in storage you need to disconnect the house battery or it will drain.
I am not sure about the starter battery and if that will drain as well. Probably not.
Although all batteries do have a slow internal drain and will die if you leave them long enough. Even without something constantly drawing power.
2014 Jayco Swift 281BHS
2015 F250 XLT 4x4 Crew Cab, Short box, 6.2 gas
Solar powered! The trailer not the truck!