On hearing about the details, Bastion decides to change tack. He asks for lamp oil and other flammables to be put into smaller, throwable, containers. He'll also take a single fair sized cask of the same, at least a few gallons.
Then he'll ride out with anyone willing to harry the oncoming group as they approach.Out of Character:
if possible, trying to time it such that the group riding out meets the undead ten minutes away from the town.