Cool idea!
What's the mold made of?
RTV silicon rubber does wonder! And if you "prep" your model's surfaces, with molding wax for exemple, you can get a bright finish out of the mold.
Another little tip (works for the mold, and for the pour) when you pour your resin or silicon, cast everything in one "string" and start in a flat area.
Sorry, it's not very clear. But youtube will explain way better!
Olivier.