In SH3 I think there arenīt subsimmers using only a megamod. All use GWX, or LSH3, or WAC, or NYGM, and add other complementary mods. The same with SH4, except there arenīt many complementary mods. Mainly, there was very little work in "candy eye" in scenarios; the bases are not so detailed as in SH3 and the equivalent of Merchant Fleet mod for SH3 never see the light for SH4 (the Japanese Merchant Marine mod).
Regards.
Fitzcarraldo