Depending on how the regenerative braking was balanced with the brakes in the MH, it could be possible to produce a lot of electrical power.
The dinghy vehicle could not only be used to brake itself, but could also contribute some braking ability to the motorhome towing it.
There's a lot of kinetic energy in a 30,000 pound motorhome rolling down the road at 75 MPH! :B
Naturally, this would be limited by the capabilities of the dinghy vehicle: Most regenerative braking systems fall back on conventional service brakes whenever the amount of braking required exceeds their ability to convert it all to electrical power.