Re: glass screens, Diwan Bhathal taught me that a homemade plexiglas screen works almost as well. It's not so bright, sure, but it truly cannot be broken. I did my 5x7 Yosemite trip with one that we scratched up with pipe compound at Diwan's place.

Still, I think you'd be better off scale focusing. If you get as hot and sweaty as I do when biking then you'll not want to duck under a dark cloth and screw around with ground glass. The crown gives you many focusing options, perhaps that is best. It is also inexpensive. But it is heavy.

But a pinhole.... nothing to break, nothing to focus!! Hard to beat! Put some fuji fp3000b45 in there and off you go!