I'd highly recommend the dry storage facilities at Marina San Carlos (called Marine Seca - "dry Marina"). They have steel casings between every boat to prevent a domino effect disaster. It's a family run business that's well respected throughout the boating community. Near to Guaymus for flying in/out. It's $4.08/ft per month, plus a haul charge - see the website.
Regarding your tank, I think you may be able to snake a tube or hose down the fill and under the internal baffles to the low point, although I have not done that. Maybe you could try with a "fish wire" first - you should be able to hear/feel it near the outlet fitting if you're successful - then switch to a tube. Also, I haven't opened my tank but I think there is just one baffle in the middle - try tapping the side of the tank and you should be able to hear where the baffle is. If you've got the tank run down near empty you could also just disconnect the outlet line, drain the last bit of fuel, then remove the valve itself and swab the deep end of the tank out through that hole.
Good luck with it,
Craig, SN68 Sangaris