[Sylvester]

Personally, id think bl wouldnt be the best, because even a brushed rock crawler has power, and i think that a bl motor would be less effecient and heat up, although you said you'd use a 11-13xl, i dont think you'd be using more than 10 cells in a crawler, and the lower cell count on low turn motors (such as a 13xl) will overheat due to their low rpm range, and i dont think there is gearing low enough to make it efficient enough to run on.

Than again, its all worth a try, you just need lots of $$ to experiment.