I don't see any problem with pre-brining. It won't leak out. Think about all of the chickens/turkeys etc that are injected with saline, for god knows how long before we buy and cook them. If you can vacuum seal, that would be a nice touch for transporting and storing on your trip, but you can get away without it if you don't have a vacuum sealer, just wrap in plastic.
The only issue I've seen with brining in advance has been if you are using Pink Salt or TenderQuick to achieve a faux smoke ring. Even after the brine has been rinsed off of the outside, the nitrites/nitrates continue to move their way into the center of the meat over time as it sits. This may (or may not) be undesirable for what you are smoking.