Nicholas 'm Boy,
Why you'd want to ski on sandy -30F snow is beyond me. Very slow going. But if'n ya gota then ya gotta.
Ya need a double plastic "Telemark" B/C ski boot like the Scarpa T3 fer real cold weather. Get the loewst, most flexible double plastic boots out there. (Scarpa T3s as far as I know but I've been wrong before.) Plus, get a FULL insulated "supergaiter" that entirely covers your boots. Nothing less will keep your feet warm enough, even with those fancy new double boots
And DO NOT forget to remove the boot liners & put 'em in yer bag at night. You probably already know this trick but I say it anyhow B/C..."Froze Toze" are ugly and painful.