If the TC is at home and in router mode as the main router of the network, get someone at home to give you the current public IP which will be on the summary page of the airport utility.
With the public IP try and access it by typing the IP directly into finder.. go.. connect to server.
AFP://publicip.
If you have setup WAN access it will. Otherwise no.
For BTMM and iCloud access and its various issues.. this thread may give you some ideas.
https://discussions.apple.com/thread/3699096?start=0&tstart=0
If the icloud method proves unreliable and you are dependent on access to the TC.. I strongly recommend better and more reliable access methods.. in particular buy a VPN modem or router.. whichever suits your internet type and put the TC in bridge behind it. Direct connect to the TC via the vpn.
You will need either a static public IP which you purchase as an extra from your ISP .. maybe via a business account or setup a dyndns account which are readily available.