Please understand these pictures are from my very early attempts to modify the TC case. I have completely changed the way I work on the baseplate now. My methods are far less ‘agricultural’ and far more streamlined with some specialist tools & techniques I have created. I have no intention of sharing THE NEW hard won methods, as they cost me hours of my time and hundreds of pounds in materials. The pictures shown here will work very well but will need lots of cleaning in between each task.

The baseplate gets a decent air inlet hole... here’s how...

Drill a pilot hole in the alloy base and rubber mat beneath.  Position is the centre of the cooling fan after it has been 'turned over'.

Brute force cutting of a 44mm hole through the alloy place and rubber mat below.  My left boot and weight holds it all in place!

Dremel sanding wheel for detailing. Keep it on its slowest speed.

Alloy and rubber mat before detailing.

Large hole has been detailed.  10x screw holes marked with blue marker pen.

A 5/32” hole punch and NOT the 5mm one responsible for the holes below.
This makes the much smaller rubber pieces that are used as ‘plugs’ in the holes afterwards.

What the rubber mat looks like afterwards. (5mm holes)

With much smaller holes punched out and re-inserted, they are very hard to see. Finer Stainless Steel mesh used here.

Fan re-assembled into the base plate.  The top opening is fully closed with tape (extra piece shows as light grey).  
It now blows into the PSU. The ‘tape patch’ on this fan is made up with two clear pieces of tape and then a strip of magic tape to hold down the edge nearest to the sponge gasket.
The patch ensures the air drawn in, primarily blows into the PSU and not sideways around the edges of the fan.

Assembled with the rubber mat about to be stuck on. This double sided tape is super sticky.
You get no ‘second chance’ when applying the rubber mat - in must go on first time and it must be correct!

A TC with smaller punched holes for the 10x screws, filled with the small rubber pieces... almost invisible!

The plastic feet shown here raise the TC by 8mm from the flat surface.
Very usefully compared with the earlier 5mm feet, this makes the TC run 1 degree cooler! (Every little helps!)

Within this picture there are 3x screw heads covered with plugs of rubber.
The ‘GR’ is the customer’s initials for identification.
Basically, the cool air goes in here...

... and come out of here.
This helps to release the hot air blown through by the now working fan.
This modification helps to reduce the temperature by 1 degree C, compared with an identical situation without.

Good airflow is key to this modification. See ‘Just FYI’ for how effective on the Infra-Red pictures.