"I used 4x4's as the mounting surface for the slide flange since these would not be covered by anything. The verticals are toe nailed into the beam below with 3.5" deck screws and are attached to the horizontal with 5" lag bolts. I was having trouble finding a joist in the ceiling above to attach to so I drilled a small hole right next to the top 4x4 and stuck flattened out coat hanger through it. Then I went in the attic and located the hanger which had, thankfully, come up right next to a joist. So I went back down below and put two 7" lag bolts straight through the 4x4 and into the ceiling joist above; that thing is solid!"