I'm considering taking Southwest for the first time for a flight from Des Moines to LV on Dec 1st and returning Dec 5th. I'm a man of size and am a little apprehensive about not having an assigned seat (and not paying for the additional seat as I fit in one, just not comfortably). If by chance there is anyone on here that has flown Southwest out of Des Moines to LV on a Monday (I know, pretty specific), how full is the plane? Typical sold out? Also, in general, if I purchase early bird checkin, does that assure me a good seat choice in an empty (to start with) aisle? Thanks all!