I had to empty my van for a service and as bit of curiosity weighed everything and also included the leisure battery and motor mover as part of the payload.
The Familia 320 has a MIRO of 750kg allowing 150kg for the standard MPLM 900kg. All the basic stuff that always goes in our Eriba came to 141kg leaving 9 kg for when it is loaded with food and clothes .
Fortunately I upgraded my plate to MTPLM 1050kg, that now gives me a total of 159kg so it's no longer an issue.

It's the motor mover and ancillaries that really eat into the payload..

Most WWB have very poor payloads and looking at what some take with them I would assume most are over the payload.