If you have a form of cutting, welding and access to materials then anything is possible and I cant see them being very complicated. We were thinking of making up a set...but decided I would avoid sliding on trees and rocks instead!
Since posting the above thread I had a rake round in me shed and turned up a 6ft length of 80x40x5mm box So I am now half way towards me pair of rock sliders. Will get another length at the weekend and make the other side & sort out the brackets & tubing..