Start by printing the front and back clips. The openscad files produce
only one side; you will have to use your slicer or printer control
program to make a mirror-image part for the other side.

Bend your aluminum bars so they look like the model in
chamberbends.scad. The first bend is at roughly 30cm, the next 23cm
after that, the next 6cm after that, 15cm, 6cm, 16cm and 30 cm
again. Most of the bend distances are approximate, but you'll want the
15cm central flat space pretty accurate because those are the bends
that clamp the chamber onto the body of the printer.

Cut two pieces of mylar 30x40cm and another two 20x40 cm. These will
be the side panels of the outer chamber. Attach with packing tape or
equivalent; trim at the bottom to clear whatever your printer is
sitting on, and crease outwards at the sides that hit the printer. The
crease makes something of a seal and also gives the panel some
rigidity. Cut two more pieces approximately 35x60cm and 35x70cm. These
will be the front and back panels and should be attached with velcro
on at least one side so you can take the chamber apart and have a slit
for the filament to pass through. You won't need a continuous strip of
velcro (you'll have trouble getting things apart if you use that
much). You may find that you can do this more easily by putting the
aluminum onto the printer and cutting to fit.

The aluminum strips for the outer chamber slide onto the printer
between the heads of the two screws at the top. This lets you make
sure to clear the bed with the rest of the pieces with minimal dead
space.

Meanwhile, the printed chamber back clips fit onto the X carriage
(make sure not to interfere with the belt) with the holes facing out,
and spaced so there's not contact with the frame. The front clips fit
on the big linear bearings (see picture) and just clear the frame and
the extruder and fan.

Cut two pieces of coathanger wire or equivalent 17.5cm long and slide
them into the back clips. Then cut a piece of mylar about 20x35cm and
use foil tape to attach it to the wire using foil tape. Crease
downward on the parts that extend past the supporting wire. (This
should trap some of the hot air around the top of the part being
printed.)

Cut two more pieces of coathanger wire 23 cm long and one piece 28.5cm
long. The two shorter pieces go in the holes on the faces of the front
chamber clips, andthe long piece goes on the open slots on the top of
the clips (you may need to pick out any bits of sagged extrusion for
it to pop in). Cut another piece of mylar about 25x35 cm and attach to
the wire using foil tape. The mylar must not extend past the long wire
or it will interfere with the extruder. Crease down the parts the
extend beyond the supporting wire as before.

Check to make sure there are no interferences.

You can remove the outer chamber simply by lifting it up and (if
necessary) undoing enough velcro so you can keep the filament in
place. To remove the inner chamber, pop the front crosspiece out of
its slots and pull out the front and back support wires. The clips do
not (as far as I can tell) interfere with the operation of the
printer, so you can just leave them in place.