Boyko,
You can use the “npm install node-red-contrib-s7comm” with the –prefix option to point to /opt/node-red/node_modules. ie.
npm install node-red-contrib-s7comm –prefix /opt/node-red/node_modules
From the little bit of investigation it appears that this node and it’s dependencies are pure javascript so I believe that this node will install and work without the necessity of cross compilation or anything.
Jeff