Horsebox Roof Strengthening/Padding

[catnap]

I want to strengthen the roof of my lorry so that my horse cannot get his head though if he rears. My lorry is a J reg Daf 45 and the roof is a bit flimsy for a horse that has tantrums... Any ideas as to what material to use, where and how? I already have 3 inch wall matting on partitions, behind him and in front of him, the roof is now the weakest point.

 

[iconique]

Could you make a foam pad, we used to have a section above their heads in a horse trailer that was made of a ply background, foam then covered with a leatherette - much like upholstering a chair?
The ply could then be screwed into the roof (Im assuming it isn't just a sheet across or you could put batons across to then secure to)?