oblong vehicle

Whilst this might be technically within the realm of things which might be strapped to the car's roof bars for the short journey from the allotment to the house, the bars are quite close together and this thing has a fair bit of weight and leverage, which might have resulted in damage to the bits of the car into which the roof bars are bolted, which would probably be the weakest point of the system. The sack barrow still has one of punctured tyre and both wheels still waggle, but when being pulled the effect isn't too pronounced.