I brainstormed some ideas for a burrowing factory. Its units would be bot type movement with, of course, most of them able to burrow.
Addict, light raider that can burrow
high dps, but low range and health
Reviler, Riot bot with a gatling gun
high dps and spread. capable of burrowing
Molotov, skirmisher with incendiary rockets
low arc, high aoe
Dealer, very quick engineer that can burrow, useful when used with raiders to heal damage and reclaim wrecks deep in enemy territory
low hp means it must try to outrun opponents and find a spot to burrow
Streaker, EMP rocket artillery
Disparager: Basic assault armed with two high velocity plasma cannons