A deep cycle battery will self discharge so after a period of time it will go flat. Flooded batteries self discharge much more quickly than GEL and AGM batteries.
Also, most motorhomes have small phantom/standby loads which consume power even when things are apparently all turned off and the motorhome isn't in use. Even 0.2 Amps, which seems insignificant when you have a solar panel can become a problem when the motorhome is in storage. 0.2Amps adds up to 5 Amp hours per day and after 10 days a 100Amp hour battery will be down to 50%, 20 Days and its completely flat, by the time you come back that battery could be useless to you and will need replacing.
If you store your motorhome outside but with a cover over it, get a clear panel sewn into the cover so the solar can still do a partial job.
If you store your motorhome inside, try and have it handy to a mains power source so it can be regularly charged. BUT, dont be tempted to leave it plugged into mains power permanently because this can lead to a different sort of trouble, instead put a timer on the power point so it only runs for say an hour per day.
If the motorhome is inside and not handy to a power point get someone to drive it out into the sun for a day regularly or plug it into mains power for a day regularly.
If you disconnect all the terminals on your battery remember it will still self-discharge. Be aware of how quickly it will self discharge and don't leave it disconnected for too long. Typically a lead acid battery will self-discharge down to 50% after 3-4 months of storage and flooded lead-acid batteries even more quickly. The colder the temperature the lower the rate of self-discharge so in Summer your battery will self-discharge more quickly than in Winter.
The key points to be aware of:
- how quickly your type of battery will self discharge
- how much your phantom/standby load is (how many Amp hours this is per day)
- what you can do to reduce that load to the very minimum
- If left uncharged, how quickly would your battery discharge with this phantom/standby load.