I soldered a 24 Volt Sunon MF4020V2-1000U-A99 directly to the power socket of the Filadryer S1. For the fan cables I also used some high temp resistant insulation material because the aluminium is getting hot like up to 100°C in the middle. I just need to glue the insulation tubing somehow into the corner so it doesn't bend forward when the Filadryer S1 is closed (it's just cosmetic it works as is too).

With the fan it takes much longer until the temperature rises but it's spread evenly - I measured it above and under the spool. Setting the Filadryer S1 to it's maximum 55°C it gets to 48°C after 45 minutes or so. Also since the fan is directly soldered to the 24V power socket you can hear when the PWM circuit for the heater is drawing current from the power supply because the RPM of the fan decreases a little bit then.

Update:
I soldered a simple ON/OFF switch for the fan. The high temp insulation tube was fixed by a bent metal paperclip that is fixed with the screw from the heater. I realized that when the fan is OFF the temp increases to 46°C under the spool within 10 minutes. Now when I turn the fan ON and wait another 10 minutes the heat is evenly spread and already at 44°C. From now the heat increases much faster. In the front I've drilled a hole and fixed a push fitting with a nut + 6mm PTFE tubing. Im printing Nylon PA-CF filament directly out of it. But for drying I use a cheap food dehydrator.

Check my blog post for more information on how to print with PA-CF:
https://www.schweinert.com/my-recipe-for-3d-printing-with-esun-pa-cf/