Here we go.
Well, I saw this piece of A4 size Acrylic for a couple of quid and it looked a bit similar to Searider Orange, so I thought I'd give it a go. The colour wasn't quite right, so I decided to use a piece of 316 instead.
1st pic is of the discs I cut out of the orange acrylic, with the drain plug in place.
2nd pic is of the flat brace bar for inside the void, the orange acrylic pieces used as a spacer, the 316 disc for the outside and a toob of sticky goo. I also used 2 no M5 x 35 csk bolts for the drain plug, 2 no M6 x 35 button head bolts, flat washers and rubber sealing washers for fixing the 316 disc and a M6 x 20 csk bolt for fixing the plastic spacers to the brace bar.
3rd pic is of the orange acrylic spacers and brace bar in place.
4th pic is of the finished job.