I'm a laser show provider and I'd been wondering how I was going to weatherproof my laser projectors at outdoor festivals last summer. It turns out that these covers are pretty much exactly the same dimensions as my laser projector cases, so if I pole mount from underneath, the cover sits perfectly over the case and also the yoke underneath. This means there is enough 'skirt' to also cover the signal and electrical connections stowed underneath.
I had to cut a small aperture in the front to allow the laser beams out but as the front of the case is flat with no openings this didn't present an issue.
In use, we had a torrential downpour on the saturday night which lasted about 4 hours. When we closed the stage on Sunday morning one of the covers had formed a puddle on top, all the way to the seams on the edges. Not a drop of water had come in. Very impressive, especially considering what i was going to pay to have some made up! These will also probably be going out to Burning Man festival to work as primary dust defense for when the wind gets up.