MB4 230a: Eruv Chatzeiros on a Boat (366:2-3)

Houses on a boat require an eruv to carry between the houses and the common area. What if there is only one house on the boat and the other people are sleeping elsewhere on the boat? What if the boat has no walls (e.g. a barge)?

Does the person in who's house the eruv food is placed have to contribute to the eruv food?