I wouldn't create a fund for this. Someone in the band (probably you) paid for the rehearsal room, so you should log that as an expense paid by you and shared by everyone in the band. Then on the Finance > Totals page, you will see that everyone else in the band has a negative balance.
Then as you get paid for gigs, someone in the band (probably you again) will receive the money, so you should log that as income received by you and shared by everyone in the band, and keep the money. Each time this happens, the negative balances will decrease.
When the balances on the Finance > Totals page turn positive, that's when you would start distributing the money you receive to your bandmates. You would log that as a distribution.
The Tracking Finances tutorial goes into this in more detail:
http://www.bandhelper.com/tutorials/tracking_finances.html