First Yankees series last year did not draw appreciably more or less than their home opener series against Toronto (Opening Day drew 25,000 but all the others between 18,000 and 21,000). First Red Sox series didn't top 14,000 any day.
All joking aside no matter who they play and how small their season ticket base is they are going to have issues. Playing in another state does neither their bottom line nor their fans and sponsors (no matter how small) any good. Real question is would they consistently sell out a 9,500-seat in ballpark in Orlando? I'm sure they'd sell out Clearwater or Tampa but latter wasn't mentioned.
Football stadium? You'd end up with the same challenge as London, but it can be done.