Here's the finished item:

Tooling I used:
60mm hole saw (to cut the outer skin holes for the two kettle elements and the temp gauge)
73mm hole saw (used this to cut a circle out of the bottom outer skin. It's not necessary if you use an angle grinder to cut a square hole as Vossy did, but i had it already)
40mm Q-max cutter (for the kettle elements inner skin)
28mm Q-max cutter (for the sight tube elbow)
22.5mm Q-max cutter (for the tap hole)
Pipe bender
4" Angle grinder with a thin steel cutting disc
Tin snips (or a dremmel if you like that sort of thing)
I used a pillar drill, but any fairly substantial drill will do when using the larger hole saws and the speed should be kept low with plenty of water to prevent the cutting edge overheating and losing it's edge.
Parts required:
80 litre pot form Ebay France £104 delivered http://shop.ebay.fr/catering-service-fr ... ksid=p4340
15mm polycarbonate tubing £25.09 delivered (2m length min order. I used 500mm) http://www.theplasticshop.co.uk/polycar ... 568-0.html
1\2" BSP skin fitting for the HLT drain. £7 (ish) delivered http://www.foxsonline.com/acatalog/info_AF2-70000.html
Two Backer kettle Elements £30 delivered http://www.heatingelementcompany.co.uk/default.asp
Two Backer cables £6 delivered (Ebay)
Two KM8 bearing lock nuts £10.34 delivered. (these are to secure the Backer elements as the plastic threaded shrouds supplied with them are not up to the job. (Thanks to scooby for the pointer!) http://www.bearingboys.co.uk/product.cg ... &x=18&y=14
4" Mashmaster temp gauge £33.43 delivered (or £52 with the customs charges


Plumbing fittings:
All from here: http://www.bes.co.uk/products/156.asp
1X P/N 6691. 1/2 BSP female-15mm compression elbow £1.38
2X P/N 17633. 1/2 BSP male-15mm compression straight £0.53 ea
1X P/N 16829. 1/2 BSP stainless steel tap £6.98
1X P/N 14558. 1/2 BSP stainless steel hose tail £2.35
1X P/N 19199 1/2 BSP winged female-15mm pushfit £2.98
1X P/N 7716 15mm single ring clamp (munson clamp) £0.60
Sundries:
Lead free solder and flux.
500mm 15mm copper pipe
1X 15mm end feed tee. (end feed = no solder)
PTFE tape. (use about 15 turns of tape on all of the threaded fittings)
JB weld or a washer. (it will become clear later)
2X 25mm long spacers with 5mm I/D hole, 2X 4mm screws, nuts and washers-35mm long
TOTAL COST (WITHOUT TOOLING & SUNDRIES) AROUND £245

Here we go then.

First job was to find the center and drill the large 73mm hole in the bottom. (I had the hole cutter already, it's not necessary as you can cut a square hole with the angle grinder) Then mark out and cut a 'pie slice' big enough to allow the plumbing to fit. Note that the positioning of the tap, sight tube and temp gauge are determined by the the HLT position in my brewery. This will need to be changed to suit.

Remove the insulation with a sharp knife. (you may want to get a grown up to help. I should have; as i nearly lost a finger tip!)

The outer wall of the pot is rolled together with the bottom. This has to be cut along the rolled edge and removed. I used the angle grinder to cut the rolled edge and tin snips. You could use your dremmel here.

22.5mm Q-max cutter in place to cut the hole for the skin fitting.

This is the skin fitting cut to the correct length so that it fits into the female brass elbow.

Here's the bits laid out for the tap and sight tube fitting. The lower part of the photo is the S/S tap with hose tail fitted. Moving right is a straight 1/2BSP-15mm compression, then copper pipe and tee, then the cut down skin fitting with brass 1/2 BSP female-15mm compression elbow. The upper part of the photo is the winged 15mm push fit-1/2 BSP female with the second of the straight 1/2 BSP male-15mm compression fittings already assembled.

Holes marked out for the tap and sight tube fitting.

Holes cut. The left hole cut with the 28mm Q-max for the sight tube fitting along with the two 5mm holes either side for the screws to secure it. The right hole cut with the 22.5mm Q-max for the tap.

Tap and sight tube fitting installed.

Pipework assembled and soldered. Gave it a good soak to remove flux etc (more pipe bending practice required


Cutting the 60mm hole in the outer skin for the kettle elements.

Cut the inner skin hole with the 40mm Q-max cutter and fit the element. The second element is fitted in the same way on the opposite side of the pot. They are secured temporarily with the supplied plastic shrouds. These will be replaced with the KM8 bearing nuts when they arrive.

This is the 'single ring' or 'munson' clamp which will hold the sight tube. The left one has been cut to the correct depth. Install the sight tube then mark and drill a hole to take the countersunk self tapper about two thirds of the way up the pot. Fit the clamp and secure the sight tube.

All done.

With a nice shiny plate to cover it all back up. A bit sad......maybe, but i wanted to keep it looking nice.
The temp gauge was fitted in the same way as the kettle elements. 54mm outer skin hole, but a 22.5mm hole on the inner skin. It took about 8 hours to make, but i don't rush.