Gell Cell charger

GeeTee
I've found these C-TECK chargers to be the best available. They are a bit pricey but you can leave them connected for months at a time.
Cheers
Pete

How about a small /cheap solar trickle charger like those sold at supercheap.

There's a guy on ebay selling a neat little 14.7v 6 amp 3 stage charger for SLA and Calicum DS batteries for about $50. I just received mine yesterday, seems to be quite good so far! I've got it so I'm not tying my other charger up keeping the 2 x 100amp/hr bat's topped up in the surf. I'd recomend looking at one of those. For the price, you can't do better!

I thought one of the advantages of gel batteries is that they don't lose their charge when stored. I'd expect that you'd be OK provided it was fully charged when you pack it away.