Welcome to the Pacific side of things at SubSim, TheImperialStandard
You mention having the Steam version of the game. Where do you have the game itself installed? Are you in the default "C:\Program Files (x86) \Steam \Steam Apps \Common \Silent Hunter...", or do you have the game in a different "Steam Library" folder? Second, did you delete the Save game folder after activating the RFB / RSRDC combination, or maybe use MultiSH4 to set a new Save folder location? Those are the two main issues that contribute to issues when applying mods.
With the first, the mod(s) isn't fully activated due to Windows "protecting" the Program Files folders from alteration. In the second, the Save folder holds all of the game's loading information, and will "contaminate" what you play, mixing the Stock game with any other modded versions of the game that you've played, whether you've actually done a Save or not. Also, Saving on top of other Saves will make the files so large, that the game has a difficult time keeping track of all of the information...
Last, but certainly not least, is the fact that the game uses a lot of your computer's memory, and as such, can use a "boost" if you will, from something like LAA (Large Address Aware, of which CapnScurvy has a good write-up for in
Windows10; Large Address Aware; SH4 Install. While specific to Windows 10, the same can be applied with slight alerations to any of the 64-bit OSes, including Vista, 7, 8, 8.1, as well as 10...
