Concrete block, in addition to near zero insulation value, is extremely porous. Wind, and the moisture in the air, goes right through it. Controlling humidity in such a building is an exercise in futility.
I suggest 4" of foam on the outside of the building. Two layers of 2" foam, seams staggered and taped. Add vertical furring strips and vinyl siding nailed to the furring strips. Add at least 2" foam to the roof, then roof over that. Tape the seams.
With those improvements, your largest source of heat gain will be the 1000 watts of heat from the transmitter. The existing 25,000 BTUH window unit will be too oversized to properly control humidity, so put in a smaller unit and leave that one for a backup. With that much insulation and internal heat, plus a properly sized air conditioner, the internal humidity should stay low under all conditions.
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