[Tibbs]

Perhaps add a bed floor and dummy load, either covering some weight, or made of heavy material?

For specific 'spot weights' you can but 2.5/5/10gm assorted wheelweights for 1:1 cars off eBay.

Thanks for that, I was planning on doing balsa wood panel in the back and as I'm going to make it into a signwriting van I'll put some made up paint tins and maybe I'll be able to put the weights in those.