I always leave the fat cap on. I like the extra insulation, and moisture it provides when reheating. On occassion I've been known to trim some off on toss it in a skillet until I have some tasty fat rendered down and then sauteeing some mushrooms for a morning after omelette etc. If I have to buy a packer that has too much fat I'll trim it some before the marinade or rub.
I'd probably wrap the brisket twice in heavy duty foil and toss it in the fridge, or Foodsaver it if you have a vacuum sealer. On the other hand freezing for a couple of days wouldn't hurt much if any, as long as it is packaged well, and would help keep other stuff cold in the cooler for the trip if you drive.
Reheating. Tried all of the options and the easiest for me is the oven. fewer variables, provided you don't have other family members wanting to jack up the temp for something else. With the brisket completely thawed wrap in foil and place in oven at about 325. Depending on size it should take 45 minutes plus to come up to temp, probe thermometer is really handy for this so you don't have to worry about it getting too done. If the bark seems a little damp or soggy when removing it from the foil just toss it on the grill for a few minutes and that should help crisp things up, just make sure it isn't too hot and don't forget about it.
Those methods have worked for me. What I've tried that didn't work in the past was pulling a brisket a couple of hours early with the intent of freezing it and then finishing it the day of the event. Completely thawed brisket went into the smoker and NEVER came close to getting tender. I've talked to others that have had it work, but there isn't anything worse than pulling a beautiful brisket and expecting heaven, only to get leather.
Hope you catch a break with the weather for your smoke tomorrow and have a safe trip.
You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer. --Frank Zappa
Recipient of a Huggies box!
Shut up, and cook!!!!