I leave mine conected all year, make sure the solar controle has different options for different types of batteries and it should do the corect charge. I would still check on them and top up watter a couple times while in storage. I check on mine at the begining and middle of camping season and the same with storage.. so when it goes into storage and about 1/2 way through the storage season.
I find its easier to check a little to often than not enough, this also gives you a chance to see how your solar set up is doing, the first couple months I would probably chek once a week just to get an idea if it is working like you expect and keeping the battery up. since your talking about stoage another thing to be aware of is if it is a snowy area your in, if so you should go down after each storm and sweep the panels off.