The ChuckleTent in "Digging For Dinosaurs"
It was used in a couple of episodes and first appeared in Series 4 "Telephone Traumas" when they ran away from the place they were putting up a telephone pole. They got inside the tent and walked away and gradually star
ted to speed up and run away.
It was next used in "Digging for Dinosaurs" when they were chased by Miss Fortune, they chased each other in their tents around the town.