What I came up with from an old printer box and some spare carpet and underlay is a sturdy, well insulated and easily cleaned cat cave which should be an ideal den for Ozzy. (The photos make it look like the lining is very thick. It is actually only about 1/2" covering the inside of the box and there is plenty of room inside.)
Step 1: Tools and Materials
The best tool for cutting cardboard, carpet and underlay is a heavy duty utility knife (Stanley knife) with a sharp (new) blade. I also used 'non-solvent' building adhesive for the underlay and duct tape for holding things together while this set. Also, tools for measuring and marking will be needed.
The underlay I used has a non-absorbent surface so will be easy to disinfect and wipe clean when required. I was initially going to use hessian backed carpet but then found some foam backed which I thought would be easier to bend and glue.