I am in need of an economical office and climate-controlled storage solution. I live in Alabama and as you can imagine it gets pretty hot and humid down here for 6 months out of the year. My biggest concern for office space & storage in this climate is cost of air conditioning and dehumidification, and my second concern is maintenance of the structure. I am looking for the most economical solution. I need about 300-400 sq ft of space. Not planning on windows or bathroom or kitchen.

I’ve been looking into shipping containers, and I really like the idea of a refrigerated shipping container because it seems like it would be a lot easier to keep cool 6 months out of the year, and really easy to keep warm in Dec, Jan and Feb, when compared to a non-insulated shipping container or standard backyard shed. And it seems like it would be quite durable.

I imagined installing a mini-split and perhaps a small dehumidifier if needed, and setting it to 75 degrees and 60% RH year-round. I’d also install ceiling lights down the middle of the unit. But I do have some questions since I’ve never done anything like this before. Such as: 

1. How much would a grade-A 40 foot refrigerated shipping container cost?
2. What is the resale value on these? I would plan to keep it for about 5 years, then re-sell it.
3. Should I put a roof over it to protect against leaks, rust, heat load? If so, how much might that cost?
4. What might the ongoing maintenance be in this climate, and how much might that cost over the next 5 years?
5. What might the electricity costs be to keep it at 75 degrees at 60% RH year-round, and use the lights for 40 hours a week? 
6. Do I need to be worried about lack of ventilation if I’m keeping it at 60% or less RH? (I am defining ventilation as exchanging air inside with the air outside)

Any advice much appreciated. Thank you.