By Evan Bleier An elite run blocker, San Francisco 49ers center Alex Mack has a big problem with open pores. Mack, who joined the team this offseason, has been sweating so much in training camp that quarterbacks have been struggling to grip the ball while receiving snaps from the 35-year-old. Things have gotten so bad that Mack’s excessive perspiration issue has led him to start tucking a towel inside his pants to help stem the tide. According to The Athletic, Mack has “carried a progressively larger towel with him through the first 10 practices.” Asked about the five-time Pro Bowler’s sweatin…