The air-conditioned building protects boats from damage often caused when left in the sun, water or humidity, such as bleaching, cracking and mold.

''It's peace of mind,'' said John Smith, River Forest's general manager. ''Your boat's not outside. It's not subject to hurricanes. The humidity and the UVs don't beat it up.'' River Forest grew out of Charles' hunt for a better place to store his boat.

Chief executive of Rolling Meadows, Ill.-based Charles Industries, which makes electronic equipment for the telecommunications and marine industries, Charles splits time between Chicago and Jupiter. He used to leave his 56-foot Neptunus at a boat yard in Fort Lauderdale, only to come back in the fall and find the vessel covered with debris.

''People are fed up with going to a boatyard, storing their boat and then coming back, finding paint spray and all kinds of fiberglass junk all over it,'' he said.

River Forest does not allow boaters to work on their vessels while they're stored in the main building. The marina handles only minor maintenance and repairs for boat owners -- all done outside, Charles said.Rates are about $3 per square foot a month, with a five-month minimum. For example, a 40-foot boat with a 13-foot beam would cost $1,560 a month.

Charles estimates that his rates are about 30 percent higher than storage barns that are not climate-controlled.''All everybody does is worry about their boat,'' Charles said. ``We want you to leave your boat here and forget about it.''

Some marinas in Northern states offer heated warehouses to protect boats from freezing winters. But marina leaders said it's a new concept to protect boats from Florida's summers.

''I've never heard of any long-term storage area being air-conditioned,'' said David Ray, executive director of the Miami-based Marine Industries Association of Florida. ``It certainly would prevent mildew and all kinds of things.''

The popularity of the new marina has prompted Charles to start making plans to build a second facility. He has made an offer on 20 acres west of Lake Okeechobee