Hi Tom,
Thanks for the drawings, I now have plenty of ideas.

I have the heating and CO2 equipment in the sump already (The Mazzei injector is pretty effective BTW)

The sump is made from glass panels. If I can remove the end two that will leave me plenty of room to add filter bags and a cover. However..!
Filter bags aren't something available in the UK (as usual ) All I can find are media bags.
Is this what you mean > Filter Bags If so, do you know (or does anyone else know) of a supplier in the UK?

For the moment I've just drained the tank so I can put in the substrate etc so I'll make any mods before I refill.