I understand the general use case what I don't get is where a pickup is more suitable than something like a flatbed Transit - https://i.ebayimg.com/00/s/MTAyNFgxMDI0/z/VmIAAOSw6DNcrKoD/$_86.JPG
Which has a bigger bed, a far more economical engine and is overall far more suitable as a work vehicle for carrying those kinds of loads.
Also do you not just have garden waste collection services?
Just hire the above for the few times a year you would need it. Honestly I do find it baffling.