There is no dedicated Marshall site within the SB Nation network. When we played the Thundering Herd three seasons ago in West Lafayette there was the Thundering Blog, but that site has not been updated in a year. Fortunately, SB nation still has us covered with Underdog Dynasty. That is a catch-all site for non Power-5 conference teams that don't have a blog home such as Conference USA, the Sun Belt, and such.
Underdog Dynasty happens to have a Marshall expert in Nick Lewis, and he was happy to answer my questions about Marshall here in the pre-season:
T-Mill: Holy crap the offense was amazing last year.