Another pointer:

Don't tackle the band after the dance or before the dance. As you have said, they either have too much on their minds getting ready, or need to pack up and go. So here's what I suggest. First of all, it never hurts for you to show up early and help set up for the dance. Some dances give you a discount or will let you in for free if you help, which is no bad thing. But if you are available early, you can help the band set up, carry their gear in for them, intruduce them to the other organizers of the dance. this is a great opportunity to introduce yourself, and maybe let on that you are eager to play for dances. I have found that about half of the musicians I speak to are friendly and receptive to this, and the rest are mostly neutral. I have never had anyone snub me or be critical of me. Just be confident and rememebr that they have a lot on their mind at the moment. This interaction also opens up another oppportunity, especially if you build up a commeraderie with some of your regular musicians. Some are okay with you sitting in with the band, as long as you don't use a mike and play along quietly. This helps you to learn how it feels to actually play for the dances without actually having to risk messing up badly. No pressure. Plus, you don't have to do it all night. You can take a break and dance, or dance most of the night and sit out just a few dances and play along. This also lets them hear your playing.

Oh yeah, also find out where the local sessions are and try to play there. That is how a lot of musicians network.

Hope this os of some help.

BeauD