I guess the big question with the "half a culvert" (as my neighbor refers to them) is whether you install the mechanicals first and spray over the EMT, unistrut, air piping, etc, or do you attempt to do it afterwards.
My thinking here is that you mount the unistrut, and a few other critical pieces that will require either picking up the stud end of the bolts that hold the building together, or require you to put additional bolts/screws thru the steel from the outside, then spray, then finish up the work. Quite truthfully I see it being a mess anyway you go about it.
Charles