The Rally 2007 is for all RV's.
The RV.net Class B Rally is for Class B RV's.
Both are connected to the RV.net group which is part of Affinity Group Inc.
I haven't attended "The Rally" but I expect that it must be really fun to go to. Affinity Group Inc. owns: Woodall's, Good Sam Club, RV.NET, Camping World, Trailer Life Magazine, MotorHome Magazine, Camp Club USA, RVtoday Television, Coast to Coast Resorts and more so you know they have what it takes to host a great event.
Some Class B Motorhome manufacturers also host rallies for their particular vans.
Roadtrek International Chapter of the Family Motor Coach Association has a list of upcoming events here:
Pleasure-Way's annual rally will be in June this year. Leisure Travel has an annual rally.