Kept me guessing as I recognised that voice -- and it's Captain Stottlemeyer from Monk!
So the brothers are scared stupid by the evil trucker 'Rusty Nail' who has just erupted through an ice van and almost crushed their car. After apologising multiple times, the trucker leaves them alone and they return on their mission to pick up Venna. They don't tell Venna about the little prank, but Lewis has not 'compartmentalised' the whole situation as well as Fuller, who seems to be getting on better with Lewis's girl.
While Lewis is in bed early, he receives a call from Rusty warning him to check on his brother. They leave the hotel in a hurry - but reading graffiti on signposts Fuller stops and they check the trunk to find their battered old CB radio kit.
The evil trucker plays some more pranks on the boys - using Venna's kidnapped friend as bait, before he tells them to meet him near a corn field at night, when he tries to run them over and then also kidnaps Venna. To get her back the boys must go to a motel room at midnight - like they did to him, with pink champagne. He destroys their car so they need to hotwire and steal a new one first.
At the room, Rusty has tied up Venna and rigged a shotgun to the door so that when the boys enter it'll kill her. In the next room Fuller manages to get outside and check the scene where he warns Lewis not to enter but is grabbed by the trucker. As they wrestle he falls and pierces his leg on a metal pipe.
The cops show up and Lewis, while outside trying to help his brother, manages to get back inside and protect Venna from the gunshot just in time. He then races back out to rescue Fuller from the truck's path that slams straight into the motel. The driver inside is dead and is identified as the ice trucker from before.
While on the final leg of their long journey home, the boys check the CB for police patrols but hear Rusty Nail's voice again, knowing that he got away.