If you have the possibility out there, I'd cool and slice at home and then vacusave it. Then just dump the bags in boiling water for 20 min, slice open and viola - perfect.
If that won't work, I would consider slicing it cold out there and putting the slice into some juice and heating them up covered tightly.
There is one other way I really like to heat up brisket, but it's a bit time consuming, but might work out there. Big ol griddle, nice and hot, slap on butter and drop on a cold slice, heat about a minute and flip. One more minute... oh man, getting hungry just thinking about it. Time consuming per slice though, but daaaaaamn.
Neil -- "Easy Bake Master"
NB Bandera [gone to heaven...conveniently located in Long Island, NY]
Rebel 23, WSM A, WSM B, UDS, Easy Bake Oven
Pork Pistols BBQ
MOINK...It's what's for linner.