I have exactly the stuff you need on this, I posted it on recycleur net, but just found it down. let me dig out the stuff when I get home,

What you need is basically, a length of 160 mm drainpipe stuff about 400 - 500 mm long (hardest bit to find), some SS mushroom headed M8 Screws and washers (B&Q), either a SS backplate, A Buddy plastic backplate, or just a couple of strips of stainless steel.

It all goes together fairly easily, and feels quite nice underwater. You can use proper pony clamps, or I actually used buddy twinning blocks (for a 7 litre).

Like I say, I post details later, but V easy to do.

Dave