Call me crazy but I too use the pistol a lot of times. It's nice not having to worry about reloading, running out of ammo, etc. (Trando: "Cursed weapon, always out of ammo!") Plus it's accurate and seems to do more damage per shot than the rifle. I use the anti-armor attachments for taking out the turret gunner in the first mission and the bowcaster or concussion rifle (which ever I picked up on the mission before) to take out the first horrible heavy weapons Trando, then pick up his heavy repeater to take out the second one.
For the catwalk trap, I find it most useful to get in a corner next to the hatch and then send a Commando to set the charge. If I set the charge I always find myself being shot in the back.