I’d rather spend a weekend the way I want to. Since it’s organized with a poll to know people’s availability, it’s not as simple as saying I can’t make it during one weekend.
Just respond for all weekends that are available to choose from, that you're not available then. If someone asks, you can say that you've planned out your weekends with your family/friends/spare time activities or that you are not interested in this trip. If it is a holiday trip it's got to be optional. If it turns out to be an actual business trip, you might need to free up a weekend and go, that will depend on the contract you have signed.