So Wilhelm......I like the build
You appear take the power supply from the Port motor 'speed controller', as a convenient source on the unregulated side? for the single Blower Fan Motor
These smallish Pillow Fans will work in dissipating xx units of heat as measured in a reduced thermal gradient of the external motor casing temperature, however needs careful consideration
We also see that this motor in manually switched......however is the fan blowing air downwards?, or drawing heat/air from the motors casings to atmosphere?
If it is the latter, you could consider some light styrene sheeting to make an exhaust trunk over the fan square body upwards to atmosphere via a vent placed on the external face [companion-way] on deck level. Naturally whatever volume [FAD] of the fan must also be complimented as a ‘greater’ availability of free volume of air entry
If the fan were reversed, it would simply circulate warm air within the hull and superstructure
Derek