Work in Progress!
Ok, to use this, you'll need the Kossel base stand in 100mm ( https://www.thingiverse.com/thing:2024677 ).
This thing holds two 80mm fans and comes with a holder for filterfoam, too. I've got two cats and I don't want their hairs inside, so I'm building up an enclosure ( https://www.thingiverse.com/thing:2840879 ) for my printer and use this to cool the inside-mounted power supply and motors. I will also create a fanduct in future to cool the drivers and mainboard, too, using one of the fans applied on this thing.
Dual 80mm Fan Holder v2:
The main part. V2 indicates an additional notch for Filter v2. You can screw two fans to it.
If you decide to put your power supply on the inside, you have to cut a part of the holder (see pictures) to be able to put the mount as far right as possible, or else one of the fans will collide with the PSU.
If your PSU is on the outside or somewhere else, you don't have to cut anything, as you will have plenty of space.
It's recommended to close the space between the base stands, so most of the air will flow around the motors and mainboard, or else too much will be wasted. You don't have to worry much about the heated bed, because its isolated on the bottom side.
It's designed to fit in the notch of the lower 2020 profile and be fixed by screws to whatever it is you want to use as wall between the stands. I'm using 3mm PVC foam plates, which you can cut with a sharp knife, drill holes through and so on.
Single part filter holder for filter foam.
The filter parts are designed to be easily removed for cleaning. I had an idea to glue magnets to the two half-circled parts of this holder. On the bottom there are noses, which will fit in notches of the fan mount. Currently you'll have to drill a hole into the fan mount and screw in something the magnets will hold on, so the filter won't fall out of it. Or come up with your own idea :D
Since this is the whole length as one part, it's tricky to print if your only printer is the Kossel which this thing is made for ;) If you got another printer with at least a 22x11cm square bed, you'll be able to print this pretty easy, lying flat on the bed. I tried printing the whole length filter on the long side vertically, but it didn't came out well enough, so I made Version 2:
Filter Holder links v2.stl and Filter Holder rechts v2.stl:
Left and right side of half length filter holder, version 2. On the backside of the knobs in v2 is a square hole, so you can glue or melt in a small neodymium magnet. Use a Woodcarving tool or adjustable soldering iron for this, I used 200°C to push the magnet in and 100°C to sculpt some of the plastic around the magnet, so it would hold tighter.
Half length so it will fit lying flat on the Kossel bed. Plus I added an overlap on the outside edge for a better fixation of the filter foam and made them thicker for two layers of filter foam (assuming the foam is 3mm in height).