I've recently got an offer to open a seed bank, which I'm considering. Have to say if I do it I'll be looking at some kind of budget option as the markup on seeds is crazy.
You could try using some modeling putty to plug the gaps in the case. Something like this http://www.amazon.com/Games-Workshop-Citadel-Modelling-2-Pack/dp/B0035VVW9O/ref=sr_1_5?ie=UTF8&qid=1291756647&sr=8-5