Adding weight to a Farish Presflo

[Vanders]

The Farish Preflos are so light that it's almost as if a gnats fart is enough to derail them! Has anyone attempted to add weight to a Presflo, and if so how did you do it? The most obvious solution seems to be to put some "Liquid Gravity" inside the hopper, but I don't fancy trying to pull apart the wagon or drill holes without some idea of what I'll run into!