I would like that too! Would be a nice little "mod": Helmets always on yes/no.
try adding forcedTorso: 2 in STR_NONE armor in armors.rul in xcom2
i know in ufo coveralls have 2 torso types for male and female and i think in tftd is essentially same thing except is land and water torso. you can force either 1 torso using the above command.
i'm not 100% sure just try it out and lemme know if it works.
Another feature request: would it be possible to have a land-only label for weapons as well as a water-only one?
would be nice t also have a land only restriction in addition to default tftd. i know is not default vanilla game but it makes the whole package complete and is very nice for modding to be able to restrict weapons both ways.
maybe
underwaterOnly: 0 1 2
0 and 1 function as regular true false values and 2 just a land only extra thing
as well as
movementType: 0 1 2 3 4 (not fly, fly everywhere, slide, fly underwater only, fly land only) . i think that's right.