Gas locker door leaking

R and R No1

we have just recently picked up a brand new sterling sport 514 and discovered that the gas locker door doesn't seal properly at the bottom middle area. When the van is under tow and its raining water blows up inside soaking all the contents and floor. Its
been back to the dealer for repair but on return has been  just as bad. Has anyone ealse had problems with this model.