I fail to see how one load of dive kit (even when wet) can weigh more than four people.
Yes you may be knackering the suspension if all the weight is on one side of the car and it lives in the car permanently but I somehow doubt that's the case.
I used to own a Rover 214 (the "rounded" version not the old old shoebox type) and that regularly had 3 divers and kit in, now that is overloading....and uncomfortable.
Anyway.....if Dad insists on buying you a new car then a twin cab pickup with a hardtop would be very nice
