The way I cob a bike together, I set my cooler wherever I want. I would remove the parts that are in the way of the cooler. If say the rec is still exposed to the air flow, I can glue that sucker on a down tube, I don't need a drill, a punch, a mark on the paint when I'm done gluing things.
It goes something like this... I've experimented enough to send this glue to the next problem child. Look up 'amazing goop' brand and figure out how to mount the rectifier with glue and the oil
cooler with glue. This ain't your momma's glue. This is chopping thru chemistry with less weight on the bike is some wrench size I don't need.