[strath76]

A good idea but it does take quite a lot of time to manage. My suggestion would be to base it on a system that allows members of the forum to purchase a certain number of packets per year (perhaps on calender year), but to allow additional packets to be 'traded' for donations. An example would be to allow the purchase of 5 packets per year and then to be allowed to either purchase or receive free seeds for seed donations. For the later exchange I am thinking that for every 3 packets of seed you donate you get 1 packet from the seed bank.

The idea behind this is that it encourages people to donate seed and doesn't rely as heavily on a few people consistently donating to maintain the seed bank.