I agree with the poster that said to maybe take the time to get your hubby more involved in the sport? With three on team, you really need both parent's support at 100% or you are definitely going to run into issues. Perhaps if he spent some time in the gym with you, watching the kids progress, volunteering, etc, that would get him more excited or interested? It really is an admirable sport, if he takes the time to really watch the kid's progress, I think he will be impressed at how strong and determined they are and also how much fun they are having. I would try this first before accepting any further commitments, especially a board position, that is a huge responsibility and I think it's important you get him on board first.
Luckily my husband is 100% completely invested in DD's gymnastics, no matter what the time or money commitment may be over time. However, it's b/c he has respect for the sport, he's proud of what she can do and how it is keeping both of our kids in good physical shape and keeping them busy. However...my dd had another hobby at one time which she recently gave up to focus on gymnastics and hubby did NOT like this hobby or have any respect whatsoever for it, and he did resent the money it costs and the time we put into it. It did cause problems in our marriage. When dd decided to give that hobby up to focus on gymnastics, I was a little sad but it has honestly been the best thing ever for our family.
The bottom line is as moms we ALWAYS want to put our kids first. But if your marriage is something you want to preserve, and you are unable to get your hubby on board with the full time all in gymnastics commitment, as a last resort, you may have to compromise and look into putting the kids in a less intense program (Xcel, AAU, rec, etc). I know you don't want to do that and I wouldn't either, it's a tough boat to be in, but if it comes to that, it may be something to consider. Hopefully once he feels more involved and learns more about the sport, he will come around!