I went ahead and made a build guide video on a neat bunker engineer build one of my guildmates made. He has an extensive, well-written post on his site at http://www.barrowdev.com/?p=562
It’s a really neat build and quite fun to play. Really high learning curve though. Rewatching that video I see so many things I could have done differently to do even better (particularly I need to work on using the Rifle even more; and even more particularly using Overcharged Shot just to clear off immobilize which is a big killer against me).