Cheers Jake for the info. I am now in the process of making it. This is what I have done so far......(You'll need to log-in to see the pictures!!)
Thick card for template....
![](http://www.maxumownersclub.com/forum/attachment.php?attachmentid=1155)
Draw round underneath adding on some extra to rest on the lip.....
![](http://www.maxumownersclub.com/forum/attachment.php?attachmentid=1153)
Cut out template to check it fits....
![](http://www.maxumownersclub.com/forum/attachment.php?attachmentid=1157)
Then the plywood base.....