Hi,
I I recently installed a version 4 of OMV on a raspberry Pi and of course one of the things on my list was an easy and secure remote control of the various elements of the software.
My setup is OMV 4 with 6 dockers so far, plugged in on the Ethernet pot of my router. After an unconvincing experience with duckdns and opening some ports to access my router, I came across remot3.it (https://remote.it/ )and I must say the experience is baffling AND free for a non-commercial account. 
Without opening any ports I access my Raspberry PI from outside, on PCs or on my mobile, very fast connection (useful as one of the containers is piwigo -> big images). The installation was really simple, I am not an expert, and the support adequate.
It is so perfect for my use that it feels almost too perfect to be true and I suddenly am a bit suspicious of the safety of my data. 
I would be grateful is anyone could let me know if they experienced the service and if they can confirm that this is safe, I can't see any threads on the subject in these forums,
Many thanks,
Stef