I *think* I understand what you're saying. Since you aren't charged fees in the summer, you end up paying less fees over a whole year if you go the 10+2 way? In that case, it's going to come down to running the numbers. You'll have to see whether you're saving more from avoiding fees or from the small amount of interest you'll be able to earn.
Check out
this post for places to stash your savings if you choose not to defer.