I started with Node-RED 1.0.6 on a Raspi 3, but decided to try out other systems, too, and have managed to install it on a Openmediavault (OMV) NAS version 4.1.35-1 and also the new 5.5.4.
Since OMV is Debian based, it's rather simple:
First you have to activate user home directories in OMV in the settings tab of the user menu:
Just select a defined shared folder.
(At least I had this already activated and the home directory of new user points to this shared folder.)
Then create a user (for example red) in the OMV webinterface, give it access to the groups sudo and ssh and change the shell to /bin/bash.
Then login via ssh or the console as this new user and install curl and maybe git for nodes not already available via npm.
sudo apt-get install curl git
Then install Node-RED with the standard script
bash <(curl -sL https://raw.githubusercontent.com/node-red/linux-installers/master/deb/update-nodejs-and-nodered)
and after manually starting
node-red-start there you are: http://nas:1880
Install additional nodes like dashboard via "manage palette" or
cd ~/.node-red; npm install whatever as the user you have created for Node-RED.
Dont't forget to enable auto start after reboots via
sudo systemctl enable nodered.service.