David hit on the head. I would make sure you have a copy of the FFL of the receiving dealer before sending the firearm. I would also recommend you put a copy of the receiving FFL with the firearm when shipped.
I have shipped firearms direct to FFLs via FedEx main depots. But some FFLs will require you to send from an FFL. Seeing as you are recieving a firearm in trade it might just be easier to work a deal with your FFL for this though.