Minisplit heating/air-conditioning units with several heads is probably way more efficient, and would give you a/c for those days you might want it. SOme might have trouble on your coldest days, but still can work in many locations. That may not be a big issue, except for potentially keeping it above freezing in the winter when not occupied (then, you'd probably want to winterize it, and then wouldn't care so you could shut everything off). On these, one watt in can produce 3-4W of heat, much more efficient than resistance heating, and they're efficient should you want cooling as well. These things have gotten much better in the last 5-10 years, and are a good choice many places where they weren't before.