The bed in the back of the Vigo is designed to carry a load. The suspension is tuned accordingly.
Without any load in the back, the vehicle seems to be very stiffly sprung and hence the bouncy ride.
You could go to a decent Kamani maker and ask him to remove the smaller Kamanis (leafs from the rear suspension) to reduce the spring rate and soften the ride.
However, this should not affect the setup in a negative manner (the remaining leafs should be properly secured).
I would request further input on this from other pakwheelers before trying.
This is just my point of view.