As a teacher and the PTO Pres. this past year, I can honestly say that many teachers got a little put off when originally asked to do anything "extra" since their main focus is, and should be, educating our kids. However, I think one thing that helped is to have a sense of humor and to have at least one teacher that is able to speak to the teachers (either at faculty meetings or through the school email, if your school has it) so that the teachers are aware of what you are doing/planning and how it will benefit them AND more importantly their students. This year I offered to tap dance for anyone willing to agree to sponsor a basket for our fall festival - several teachers took me up on it.
At our faculty meetings I was able to take a few minutes, with our principal's permission, and tell them what was going on or what a success the last activity was and thank them somehow for making it possible.
We did not require a teacher rep from each grade level, although I've already been told this year that several grade levels have decided amongst themselves that they will have one this year and have told me who to get in touch with (that's a HUGE step for us).
Lots of communication and a sense of humor is what I'd recommend.
Deb