He has the Steam version, and as such, you cannot use sober's mod, which I have wanted to try, but I have a Steam game also. But The Wolves of Steel is a very good mod, and is very customizable, and I am able to get just about what I want in the mod. The game is worlds different from SH3, other than the subject matter.
The game, if you did a default Steam install will be in "C:\Program Files (x86) \Steam \SteamApps \Common \Silent Hunter 5" folder. As such, if you desire to mod, this location will usually NOT work. The Program Files folders under Windows are protected, and as such, any alteration performed in there by JSGME or similar will be rolled back to their previous condition to "protect" the user from themself... very frustrating. SH5 can be used there if you defeat all of the UAC (User Access Control), which is generally not recommended. If you have Windows 10, any alterations to your system that you make, are rolled back to what Windows knows you want after any major Windows Updates, so that can be an exercise in futility some times.
Refer to "
Moving a Steam Installation and Games" for info on accomplishing a move. If you only have one or two Steam games, it is sometimes easier to uninstall Steam, then re-install, but pick a different location to install to, such as "C:\Games \Steam etc." If you have a good second hard drive in your system, including fast external drives, then you could use that as a 2nd Steam Library folder, and install the game to there. Steam is not too much different than a disk install, and definitely better than the UPlay version of the game, but it does have its own "quirks" to deal with.
