If your 5th wheel isn't real heavy, you could wait on the bags. When it comes to installing order, they both connect to different locations so it doesn't really matter. I would also recommend 5th when brackets designed for your specific truck though. Makes installation easier then the universal brackets.
2005 Silverado 2500, Crew Cab Short Bed. 122,000 miles
MODS: AFE intake, LBZ mouth piece, MBRP cat- less exhaust.