Try this set on top of GWX and SH3 Commander:
TKSS18 German U-Boats Compilation No Eagle
http://www.mediafire.com/file/ksy4ji..._Eagle.7z/file
FixAllSubGWX
German UBC_FuMO_Fix_SNS_GWX
http://www.mediafire.com/file/9k00yz...or_GWX.7z/file
New U-Boat Guns Fixed reworked (For German U-Boat Compilation)
http://www.mediafire.com/download/cd...mpilation).rar
No need for MEP in my opinion, nor other mods, but if you still want to try them, activate one by one with tests each time to find the CTD culprit...