We had a VSB for a while too. I bought the one with the external light sensor, so I could mount the VSB inside the coop to keep it out of the weather.
We had the motor burn out, which was replaced by VSB free of charge (in hindsight, I think the door may have frozen shut, so it was probably our fault!). The replacement unit worked well for a while, but then the hen house roof developed a leak which also got into the VSB via the mounting screw holes and killed it (a small drip in had nowhere to get out, so the whole thing filled up inside!!).
We now have a super whizz bang door opener which I designed myself, and which uses an industrial programmable logic controller (we sent men to the moon with less computing power). This also brings the lights on in the henhouse a couple of hours before when it thinks dawn is going to be :-)
Regarding pop holes, I wanted something that wouldn't warp or stick easily, but also had a bit of weight to it, so I used an 'eternit' fibreglass slate. I'm sure you can get them to send you a free one-off sample too ;-)
HTH!