im installing the new front box frame rails and for those that have done the job before, is it easier to weld the rails together before puttin them in the car, or put one box rail in the car at a time?

 

I welded mine together before welding them into the car. There are some bolts that need welded in before you close up the rails though. Look at your old ones, and compare the two. I thought about going the other route, welding in the main peice first, then welding the outer peice on, either way, it should work out fine. I did paint the interior of the rails to prevent rust too.