With some modification I think these would work well in the US to keep the projector at the required height or just a bit higher for outdoor shows you could put some kind of Black material over it to make it look nice once you have adjustments done.
Scaffolding works well but its not real portable this is portable, a bit heavy @ 60LBS but so is scaffold nice thing is this rotates 360 degrees Its what hunters use when they don't have a tree to attach a perch to you will not get an equivalent scaffold or truss rig for the same price.
The gun mount would need to be removed and I think the projector could sit right on the seat 22" wide by 13" deep with a little bit of rigging to attach it assuring it will not fall!!!!. Maybe someone on PL has done this or hunts and has one to look into the idea. It can support a 300lb person so I think it will support a Laser Projector.
Let me clarify a solid state projector not a old school gas ion projector!
Just a thought
http://www.ebay.com/itm/NEW-BIG-GAME...ht_1162wt_1141