Thanks all for the advice and links!
This is the fan I use. Seal the gaps around the fan.
https://www.amazon.com/gp/product/B07VWLSMN1/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1th
That one grabbed my eye as well. Contrary to my latitude, it gets rather southern soupy here on the Delmarva coast in the summer and the water resistance can't hurt.
Meanwhile, I scared up four case fans and three 12v warts in my "junk" drawers so cost so far is zero
I spent several minutes sanding and filing the case fan to get it to fit then got lazy... a quick snip even with the outside of the mounting bolt holes on the bottom end of the fan with diagonal cutters let it slip right in to place.
I didn't seal anything because I have to go back in and remove the nicad batteries and tidy up the wiring and it will hold a tissue up to the screen as is so I may just skip that part for now and see how it goes.