shipping container workshop?

[Tenson]

If you insulate the entire container really well, it will only require a small heat input (when closed) to keep it warm enough to stop dampness. Remember that insulation will not keep it warm in itself, it just stops heat escaping so you will still need a heat source.

I used to work in a small recording studio where the room was kept closed nearly all the time and had sound-absorption over most of the room surfaces. Even just running the computer and an amp the room was noticeably warmer than anywhere else. I calculated that was probably about 100 watts of heat output keeping the room warm.