Made my own. MDF 18mm out of homebase and covered it with waterproof canvas and stapled it underneath and put a bit of velcro at the back to stop it sliding when dog jumps in. As the MDF was an offcut Homebase only charged £5. The canvas was about £15 and already had the velcro and a staple gun so £20 and done the job nicely. Didn't fancy paying the £900 for the comfort pack.
Hope this helps.
Hope this helps.