First, I doubt FedEx will ever demand you send your passport. Why not call FedEx after looking up the phone number independently.
Second, I have been asked to show my passport and visa to Thai customs officials once. This took all of 10 minutes and is good for the term of your visa, I believe.
Last I checked, banks offer up to 2.5% interest, depending on term of commitment (6 months - 2 years) with substantial interest penalty for early withdrawal.