We were hauled out at Peakes two years ago fir the hurricane season. There was advice aplenty about plastic wrapping, aircon, and applying wax to the hull and leaving it unpolished. There were advocates for and against each of these. When I asked for advice from Peakes engineering they gave no definitive answer. They cited boats that did all these precautions and had mildew and also a boat just looked and left for 3 years, that was pristine when opened up again.
Our decision. A/C was expensive to install and to pay the extra charge they make for the electricity . Our hull was 20 years old and beautiful- despite a life in the Med and various visits to the Caribbean. The boat is very well insulated, and we couldn't understand the plastic covering which would make it like a greenhouse . We decided to do non of these. We employed a local lad (recommended by Peakes - they are badged in order to work their) to go on board once a month and open all hatches for an hour, to wash the boat down, to change the dehumidifying crystals in the two containers inside the boat, and to send us an email report. The boat was perfect when we got back and we paid the same lad to polish the boat before launching.
If you use your dehumidifier I think you will be just fine, just check the charge for power. I would recommend the use of one of the yard lads to open up once a week and check things over - it is great peace of mind. I would be concerned about a dehumidifier on for 5 months with the boat shut up - I don't know how that would affect the woodwork. Others may be able to quote experience here.
I'm sure others will have different views, that was just my experience at Peakes.
Ocean Hobo SN96