OK, Steam is fine, but does require some "tweaking" to do mods correctly. Did you "manage" your Steam Library, to install the Silent Hunter game outside of the "Program Files (x86)" folder structure? Steam can be in there, but the Silent Hunter games cannot. Windows does not like to "see" cfg files changed in its "protected" folders, such as any of the Program Files folders. Let us know where you have the game installed. Also, the mods, you don't need the TMO patch if you're using RSRDC, not that it would hurt anything...
1. TMO 2.5
2. RSRDC TMO 502
3. RSRDC TMO v5xx Patch
4. OTC for TMO/RSRDC
and just to make certain, you're using this?
1.5_Optical Targeting Correction 031312 RSRDCv502
When you do mods, be sure that you've deleted the content of the SH4 Save folder in My Documents. You do not want to use any previously saved material, else you will contaminate the game, and end up with a CTD. If you are in the Program Files folder, your mods are only partially activated, and you could end up with a CTD from the game, if it even ran... Check things and let us know!
Be sure and check-out THEBERBSTER's thread
SH4 <> TUTORIALS <> HOW TO DO IT <> INFO <..., and pay particular attention to links he has marked with "
STEAM User Information"