Just paint the walls and add a 1T backup AC.
Bowling Green KY, winter design temp 10F, summer 95F.
Just for kicks, looking a physcho chart and off top of head calculations.
1 kW heat.
Electronics actually perform better at lower temperatures, some devices may have problems below 20 F, but let's put winter inside temp at 50F just for maintenance comfort.
For 12x12 building, Roof has say R-23 insulation -
Ceiling loss = 144*40F/R23 = 250 BTU/hr
Wall loss = 12*4*8*40/R3 = 5120 BTu/hr, Simple fill of block cores wit;h vermiculite or similar cut that down to 2500 BTU/hr, so no added heat ever needed.
OP says 72F in summer is OK. White paint on South wall = about 205 BTU hr gain
12*4*8*(95-72)/R6 = 981 BTU
Internal transmitter loss = 3412 BTU
Total summer gain = 4643 BTU/hr or under 1/2T AC minimum
Paint the outside walls with 3 coats of vinyl acrylic white (or thermally reflective) paint to control humidity infiltration, fill block with insulation if not done so earlier. No need for 'heroic' insulation.
3plink only needs say a 1T for backup AC. Colder is better, so only needs to control for humidity. Use a dehumidifier sensor for primary AC control vs. temp
KY summer is 95 dry bulb, 77 wet bulb equates to only 40% typical RH.
Say it is a Huston summer day, 95F 90% RH.
The AC already cooling down to 72F, which means AC coil is probably below 60F worst case.
anyway, roughly 0.03# H20 per #/ air needs to be reduced to around 0.01 #H2O per #/air.
Say 1/4 air change per hour = 20# air/ hour; or 3 pints of water per hour dehumidified by AC
Dropping from 60 BTU/# dry air down to 25 BTU/# dry air on the Enthalpy scale.
35 BTU *20#/hr = only 700 BTU/hr for dehumidification.
No need for all kinds of added insulation. Paint the inside too where easy to do if not already painted.
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