I'm about to buy my first bivy (for a PCT thru-hike next year). I'll be using it with a tarp, so I'm thinking about something with a sil-nylon floor and a water-resistant/breathable top. I've got 2 quick questions:
1) How reasonable is it to use a bivy without a groundcloth? If I get one with a sil-nylon floor, I was thinking of treating it with a silicone sealant (see http://jwbasecamp.com/Articles/Silnylon1/index.html) to toughen it up a bit.
2) Should I get a bivy with a side opening? If I go without a groundcloth, I'll be using my bivy every night, including a lot of warmish nights. The side opening seems like it would make sense since I could leave the bivy wide open on warmer nights. But, never having used a bivy, I don't know if this really would make a difference. Any thoughts?

