SES on W/ EVAP codes

The SES light has come on twice now in the last week or so. The first time the code scanner said EVAP pressure leak (small). The second time it said EVAP pressure leak (gross leak). Has anyone else had this happen? I've cleared the code both times. Also the fuel cap indicator has come on a few times, but the cap has been on tightly, however the rubber O-ring is looking kinda dried out. My guess is this is where the pressure leak in the system is coming from. But I was hoping someone else could have a clear explanation. I've got to make about a 1500 mile run to Chicago in the truck this weekend, so any help or advice would be greatly appreciated. Thanks all.