You could use construction adhesive for the cladding, just use a few screws until it dries, or if you want to bring the cladding out to the level of the brush fencing, you could screw/glue some treated pine battens to fix them to.
As for your brush fencing, screw some galv. screws into your purlins but not all the way, wrap some galv. tie wire around the screws to attach the fencing to.