One of the problems with amateur astronomy is that it is a amateur handyman/engineer's delight. There are so many ways of doing things and each of them can be right in thier own way. Go figure out where to put the holes so that they don't break the mounting of the mirror and then figure out how you're going to mount the fan onto the backside of the scope with a small battery (which can also double as a counterweight) without affecting the ability to adjust the mirror mount. That's amateur astronomy with the engineering touch at it's best.