Looked at Dometic's site, and don't see anywhere that you can specify a length, only a width. I kind of doubt a standard topper will extend out roughly 7'. Dometic does offer a "case awning" that goes over the "patio" of a toy hauler; that might fit.
But also had another thought; I think it might be very difficult to mount either of these without covering/removing the marker lights on the front of your unit. Not sure if these are required by regulation? Worth checking into.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP