Step 1:

there are three ports, the top one used to have a pressure guage and is now filled with epoxy to fill the gap.

Step 2:

Emtpy out the fire extinguisher and paint it. Then separate the to peices and drill a hole somewhere in the fire extinguisher for the tyre valve to fit in. Drill another hole in the 20 X 1.6mm aluminium plate and put it over the tyre valvle and secure with two big hose clamps as shown in the second image.

Moving on to the second piece which is shown in the first image. Grab the double 3/8" male adaptor and Using plumbing tape rap it around one of the ends. Using a shifter tighten it on the end where the nozzle used to be. You will find it hard to screw it on because the fire extinguisher has a thread that is different thread which is hard to find, so you will have to force it in as tight as you can and put some epoxy or silicon around it so it doesn't leak.

Step 3:

Using the QEV, two double 1/4" male adaptors and a 1/4" female to 3/8" female adaptor screw them all on the the QEV as shown in the picture.

You may notice some aluminium plate on top of the QEV, that is my homemade scope railing I make from the left over 20 X 1.6mm plate and some 10 X 3mm aluminium plate.