RTRR with DDNS ? help noob alert

[frownwarrior]

Hey guys
I try for ever now to do 1 simple task. copy all my files from my office QNap to my Home QNap and visa versa. So I set up an RTRR job that at begin worked... slowly but it worked but then, becasue I'm a noob it stoped working. why ? becasue I used the IP of the 2 netwroks but there are Dynamic IPs -.- so obv. after my provider reset my IP the RTRR faild. so now I tought I was clever. I setup an DynDNS service, one that my QNAP supports (t-210, selfhost.de) but what now ?
can i just make a new RTRR job and using the DDNS as "ip" for it ' will that work ? or how can I use RTRR with an dynIP anyway ? pls help me and pls as simple as possible. and don't just say. "you should check the forum first etc." or "there is this one thread that has the same Q but actually is comp. difrent problem"
I allready searched here in the forum but I didn't find anything usefull yet and my time is runing out...

so if anyone knows any help would be great.

ps. sorry for my bad english I'm a noob there too