I'm not enough of a Btech grognard to suggest a canon planet for you, but I think that's a great idea for a campaign! I little rag-tag outfit in the mountains shooting up convoys and scrounging for supplies is awesome. I ran a similar campaign with an old system called Twilight: 2000 a few months ago (set in modern times) and it was great fun.
One of my best computer-game memories was an expansion called Resistance for Operation: Flashpoint. More than any other game it really captured that Red Dawn feel of being an outgunned and ill-equipped guerilla outfit sticking it to an invading army. The open-world sandbox nature of it made it seem like you could almost anything, but almost anything would also get you killed. I've been wanting to try the spiritual modern successor to it, Arma 2, to see if it still captures those same feelings.
BTW your namesake is my favorite mech! [rockon]