Thanks trews,I'm still faffing but I have a touch of ocd and will keep faffing until it's just right [emoji6]
NoAngel, we decided to build a box into the back of the shed,the floor is unlevel,so he made a base which is about 1.5" high at one end and nearly 6" at the other so you can imagine how unlevel it was! He then positioned 2x2s where I wanted the saddle racks so they had support. The front,top and sides are 18mm mdf and the back is 6mm so it's very strong. The walls were not strong enough to load anything heavy onto anything you attached. Some parts were but doing it this way meant things could go exactly where I wanted them. He has offered to fit mdf along the wall behind the feed in so I could add more onto it,it's not too hard a job,just buy the big sheets and attach with nice big plugs and screws!Had no problems fixing mdf sheets to the stone at all. He then filled with expanding foam down the sides just to keep everything stable but he did say you provably don't need to do that he just likes using the stuff!