I live in Largo (US19/East Bay area) and I keep my boat mast up at the Gulfport Yacht Club. It's about a 20-30 minute drive. The facility is excellent and the people are great. Primarily beachcats. Locked storage and a clubhouse. Cost is around $32/mo all included (membership, yearly dues, facility fee and storage fee). We sail on Boca Ciega Bay and have two races a month (Mar- Nov) and several regattas each year. I highly reccomend it. We have several monohulls on trailers (largest is a 20). Should be a space or two available (and new ones generally open up if you are active). Here's the useless webpage: http://www.geocities.com/gycgulfport/
Next door to GYC is the Boca Ciega Yacht Club. Another friendly club that has locked mast up storage. Their stogare is more geared towards larger monohulls than beachcats. Reasonable rates. check them out at: http://www.sailbcyc.org/
Also available is the Clearwater Sailing Center. Another great facility (hosting the Alter Cup this year) but expensive. I think its around $1,000/year plus more if you leave your trailer. It's new and fancy and maybe a little closer if you live in west Largo. I don't believe you could keep a large tri their. Here's their address: http://clearwatercommunitysailing.org
There is also the Davis Island Yacht Club in Tampa. About a 30 minute drive on weekends. They have mast up for big boats and beach cats alike. They sail every Thurs. night and host several regattas a year. They are at www.diyc.org.
I'm sure there are others that I've missed
Feel free to email me if you need more info or a GYC app.