I have more in the Unistrut to mount the reel, than the reel itself cost!!! I looked at all the possibilities and with a metal building you are limited in how you mount stuff. I did a mock up of mounting the reel on the purlin using some real stout Unitstrut Ell brackets, and putting it right on the purlin flange. Had everything C-clamped in place. It looked OK, but the purlin was too flexible, so I backed up to my original plan, which is what you see in the pic. Lots of Unistrut wasted, the roof and wall purlins all require a piece of Unistrut 64 inches long to span between two of them, so between this, and the lighting installation, I have lots of 56 inch pieces left over (10 ft sticks). Lowes was about $2 cheaper per stick, theirs is cadium plated, Home Depot's is galvanize slick finish.
Forgot to add that I mounted the reel so the hose comes off the back/bottom, rather than the top as shown in several of the pics I've seen. This puts the pulling force close to the mounting bracket, and is actually tending to lift the reel against the weight. Pulling the hose off the front/top means there is an extra foot or more of leverage/force being exerted on the bracket and its mounting, and pulling it in a downward direction, with the weight of the reel, rather than against it.
Charles