For anyone looking for ideas i thought i'd share my homemade bed/shelf. All in it cost me about £70 in materials.
I wanted to make something that was
Profiles for the base:
Carpeted the top sheets of all the way round. This guide by coombe valley campers was ace
A nice tight fit
Secured the sides to the floor fixing points using some longer bolts and the original tie downs on top of the wood.
The final product, really happy with it. Also added a Nooks Board from the Ply Guys for hanging hats, hemets etc. and a Vanshades rear blind. Stealth camper mode on! Hope this helps anyone that needs something similar.