I also fly Air Tran. Love them!
The day before you check out you will receive the DME envelope on your door. In it is a letter giving you your pick up time (about three hours before your flight--in your case about 3:30pm). At the bottom of that letter is the number to call if you are checking bags. Call it, tell them how many bags you are checking, give them your credit card number to pay the baggage fees ($15.00/bag), and they will give you a confirmation number. Early the next morning run your bags down to luggage services where the DME desk is located. Give them your IDs (so they can print your boarding passes) and the confirmation number showing you have paid your baggage fees. They will take your bags, weigh them, print your boarding passes, and stick your luggage claim tags onto the boarding pass envelope. If you have any carry ons take them over to the luggage service person and they will hold them for you until you pick them up when you catch your DME bus. They will also give you a claims ticket. Your checked bags will go on to the airport and you won't see them until you get to your home airport that night. You can then go on to the parks. Arrive back at your resort at least 15 minutes prior to pick up time, go to baggage services, claim your carry ons, show either the letter you got the night before that showed your pick up time or else the travel voucher from the DME booklet you got before you left home to the DME bus driver then just hop on the DME bus. Be sure to arrive at least 15 minutes prior to your pick up time, as the time shown on your DME letter is the time the bus is scheduled to depart your resort, and they do sometimes leave early. If you miss your assigned bus, Disney is under no obligation to get you to the airport, so be sure to leave plenty of time to claim any carryons you might have. In your case I'd make sure I was back to claim my carryons by at least 3:00pm. When you get to the airport, you can go straight through security and to your gate. Your checked bags will be waiting for you at your home airport. From the time you turn them in at the DME desk at your resort that morning until you get home that night you will not have to see or deal with them.