Interesting... I'd overlooked the possibility of uneven cooling.
A 3rd option could be to build a + shaped wooden frame that sits securely ontop of the mirror box with a fan in the middle blowing at the centre of the primary. Maybe take ~30 min off cooldown time?? Then take it off.
The suspended fan using wires that is left on during observing might have downsides of diffraction effects of the wires and the fan's shadow increasing the central obstruction.
Eric wrote:
The idea of the fan in each corner works good on small mirrors, but on large mirrors it removes the heat from the mirror in a "V" shape and appears astigmatic at the eyepiece.
The fan suspended above the primary has been used successfully, even if it is unnerving at first.