There are many many things that can go wrong.
Try a different method.. direct AFP is the best. But please make sure you have all the BTMM icloud stuff correct because it is the easiest.
https://discussions.apple.com/docs/DOC-3413
If you are testing from WAN location.. which you must,, then you have to have full access via a public IP and no firewall blocking you. If you test with anything else.. and in any other way it won't work. You must have public IP, not private IP on the router. Many ISP cheat and use private IP. You must have no firewall in the router.
Even getting BTMM working is much easier with knowledge of the public IP on the WAN of the TC. See some of the other people with the same issues.
https://discussions.apple.com/thread/3699096?start=0&tstart=0