Rebecca and the company decided that they would ambush the people who were trying to attack them for whatever reason. Sure, they did not know anything about those people; however, they attacked them without warning. The chances are that beam would have obliterated them if not for John's Seed Power.
With the storm that Rose called forth, they could park the vehicle elsewhere. The storm made it damn near impossible to see. Primarily because of the wind kicking up dust, not to mention the heavy rain. A heavy haze was masking their appearance. The mask allowed them to get onto the ground, either laying down or crouched.
Still, they needed to figure out some way to cover their mouths, noses, and eyes with some kind of protection from the storm. Thankfully the truck had bandanas and goggles, so everyone used the bandana to cover their nose and mouth while shielding their eyes with the goggles. This allowed them some mild protection against the storm.
