I went Cybertech, once I find a piece of Orange gear I like the look of I can just mod it, Reverse Engineer the old mods and make some grenades. Went Scavenging as the companion gifts you sometimes get are good for maintaining decent standing, and Underworld Trading for the rare metals and, occasionally, Schematics which I can either sell or use.

For Powertech, there's a talent on Tier 2 which makes Rocket Punch a guaranteed proc of Ion Gas Cylinder. That coupled with talents that increase the duration of the DoT of the Cylinder means you can pretty much always use it whenever it's off CD. I'm unsure about how useful it is for Mercenaries, but judging b the amount of attacks they do with skills such as Unload, I'm guessing whichever Gas Cylinder they use procs quite often.