Ventilation for Boat stored on the hard

My approach is always to seal it up tightly and then fill open buckets with No Damp (or similar) and leave them all over the place. One for each cabin, head, bilge compartment, and several for the salon. They will fill up, so you have to have a secondary bucket to catch the overflow. NEVER spill that stuff inside the finished spaces of your boat. Sailors like to use their vents but I find that sealing up is the best approach. Toilets with non-alcohol antifreeze in them will have a lower vapor pressure than a bowl full of water. And make sure you remove every bit of food obviously.

For a dozen or so 6 month seasons I used to leave the 2 previous boats in the water with a dehumidifier on the galley counter with a short hose that drained into the sink that exited out the side. Never had any issues.

Pretty fail safe subject to power reliance, along with a small fan inside to circulate air.

The dehumidifier and fan will help, but I surely wouldn't leave a 55' Fleming on the hard in Grenada in the summer, the heat will destroy the woodwork.

If you use two AC units, they're the dehumidifiers themselves. Still incorporate the fans to help move air.

Best outcome is that your yard has access to a 4 ton package unit and some flex ducting. With the two 13k Btu you're at two ton, better than no ton. Should be fine for dehumidification. Won't do a lot to keep cool, but it will dehumidify. Yeah, that's probably better than straight humidity control as those just generate heat. Fans to move air as well.