Every state is different. Most states for college students attending as an OOS student will not allow them to become residents, thus no voting rights. The main reason why is if they become a resident, than they are allowed to pay IS rates and not OOS, which can be tens of thousands of dollars a yr.
The rule of thumb is your mailing address must be yr round, living in a dorm does not allow you to have yr round, thus you do not have proof of residency to register.
Check with the state regarding residency. In the state that our DS attends as an OOS student, he would not be able to become a resident even though he has a 12 month lease off campus. The reason why, is they ask one important question to determine residency. Can you be claimed as a dependent of a non-resident? He is our dependent, and even though he has an apt., and has for 2 yrs., that state will not allow it, since Bullet and I are residents in another state claiming him on our taxes. Again, the reason why is to close the loophole for students trying to save tons of money in college. To give you an idea of the amount of money we would save as an IS, it is 28K a yr difference between IS and OOS. Our DD's college is 23K a yr difference. Multiply that by 4 yrs., and every state college with OOS students; you are talking millions of loss revenue for the schools every yr. VA has @ 16 state colleges, by VA law only 25% of the students can be OOS. Imagine, if all 25% became residents just because they went to school in VA.
Personally, I think that all MOC's are accustomed to 2nd timers, and understand that they may attend college OOS. They will not hold this against you, because in the end you are a constituent paying taxes to their state as a resident.