Given these dimensions, it is possible to fit a full-size mattress and box spring in the back of a mini-van, but it may be a tight fit. It may be necessary to remove the headrests from the front seats in order to create more space. Additionally, it may be helpful to use a moving blanket or other soft material to protect the mattress and box spring from damage.
It is important to note that the exact fit of a full-size mattress and box spring in a mini-van may vary depending on the specific dimensions of both the mattress and the vehicle's cargo area. It may be a good idea to measure both the mattress and the cargo area before attempting to load the mattress into the vehicle to ensure that it will fit.
