Peace deal or ceasefire that becomes permanent will need to be policed to have any meaning. That means boots on the ground a la South Korea …

That would be wasting money, ships are expensive to charter.

Whoever operates them have every interest to have them moving about.

Yes but they can get quite close to that. And voyages don’t last that long.

Thermodynamics, heat in causes boil off but that takes massive energy to vaporise everything, and it is limited thanks to the good insulation.

Boil off is never vented, it powers the engines. They can also reliquify for some ships at least.