Our GWV Legend came with metal extenders. They are also anchored to the simulators with brackets, which I understand to be important.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)
Next: 2022 Fully-custom buildout (Ford Transit EcoBoost AWD)