xep

I also don’t see how hobbyists can install undersea cables.

Straw bale construction isn’t hay, and its characteristics will probably surprise you: https://www.familyhandyman.com/article/straw-bale-construction

Straw bales have up to three times the R-value of conventional home insulation, along with excellent soundproofing and fireproofing characteristics.

China’s good at this kind of thing, could go to them for advice on setting it up.