For ready built sub enclosures go to www.audioscape.co.uk

For the 4/8ohms set up - without seeing the amp or the spec sheet that came with em I couldn't tell ya. Try posting up the same question on the Talk Audio Forum ( http://www.talkaudio.co.uk/vbb/ ) as them boys are usually shit hot on that stuff. Remeber to include the model number and any other info you have on the amp tho