I have created a bracket and an air duct for a Chamberheater.
I only created these in the Bambu Slicer as I have not yet learned CAD.
But as long as you don't change anything, the print works perfectly (despite error messages).

I created one file with and one without insulation, as the insulation is 9,7mm thick.

In case you are wondering why the gap from the holder is bigger than the rail where it hangs on, it is because of the bump in the rail and also I put a little of the 3mm foam in between to decouple it from the rail in case the fan of the heater could generate vibrations. Also if you like you can put a nail or a screw through the hole of the holder and the rail to fix it but with the foam it sits tight on the rail and won't move.

And of course you need to cut the power cable of the heater to get it through the holes and solder a plug to it or use some Wago clamps.

You Should print all the parts from ASA or PC as the airguide gets up to 75°C

You can route the cables through existing holes in the housing without drilling (see pictures)

You need:
1. the "Mini Heater 50w" can be found on Amazon google or ebay (Just type on Google: "Mini Heater 50w" and you go on pictures and you will find the same model)
2. A 90° angled C7 plug
3. If you want temperature control, a socket with thermostat (also available from Amazon google or ebay)

I recommend:
1. For air circulation and even heat distribution:
a) https://www.printables.com/de/model/418630-bambu-lab-integrated-hepa-carbon-aux-filter
in combination with:
b) https://www.printables.com/de/model/658434-x1c-aux-fan-air-reflector-guide
This filters the air and directs it upwards, ensuring good heat distribution without affecting the print. I always set my Aux fan to 30% while printing.

2. You should also insulate the housing.
I used Armaflex 9-10mm and in some places Armaflex 3mm (foam). I also used Alubutyl under the Armaflex to improve the noise insulation.
See my pictures and also a video here:
https://www.youtube.com/watch?v=GVgW8a-ly_E&t=386s

3. In addition, I have insulated the electronics from the heat with these two prints:
a) https://makerworld.com/en/models/14051#profileId-14100
b) https://thangs.com/designer/MandicReally/3d-model/Bambu%20X1%20Electronics%20Box%20Seals%20-%20Hotter%20Chamber%20%2F%20Cooler%20Electronics%21-995214
I only printed the large plate from b).
However, the hole for the cable should be extended for the shielding plate because in later revisions of the X1C the cable routing is different (see my picture)
To do this, you can simply add one or more negative cylinders in the slicer and adjust the size.

4. I also recommend improving the mainboard cooling. This is easily done with this print:
https://www.printables.com/de/model/538932-bambu-lab-mc-control-board-fan-noctua-upgrade
Works with a stock or Noctua fan and keeps your electronics way cooler by providing fresh air from outside. Also it is quieter than the original positioning.

I also want to mention that there is the possibility to put a wire in place of the Thermal protection (bimetall fuse) or unscreew the left cable and screw it directly to the right, to only regulate it via the socket with thermostat. But that is at your own risk and I wouldn't recomment that. But here is a video of the disassably:

For the choice of filaments for which you use the heater:
In Bambu Slicer, change the printer to X1E and select the filament you want to print.
Then you can check whether Bambu uses the X1E heater or not.
For ASA printing, for example, I would not recommend turning on the heater, as it makes for unclean prints with sharp edges and also with overhangs. The chamber should have a maximum temperature of 50°C for ASA. Better 45°C
(This is why the X1E has the heater switched off for ASA)

I got the main idea from a picture that a guy posted on Facebook. But as the guy didn't even bother to answer my comment or my message I constructed the model fully myself.