Phil has an emminently sensible 4 seater (aka 2 seater+pickup bed like mine🙂) .... I carry most of what I need in suitably selected tupperware boxes (other plasticware is available) ... keeps everything dry and all together. The boxes were selected to slip into the space under the seats (I have the wooden 'seat-risers' so there's 'wasted space' under there) ... safe under there as the crossmember stops anything sliding forward under braking.
K