Dully? 4x4 or 2x4?

[flyinbullmax]

Thanks Guys, yes we had a Nice Christmas Eve party with the family. Thanks for the advice on the hitch I'm going to contact my Curt resseller next week. He told me about the new US bylaw about the installation of the cross rails, saying that if I have a plastic bed liner, its illegal to install the rails on top of the liner, it has to be fixed metal to metal in the bed. Did you hear about that?
And for the engine brake do you guys have advise on it? Should I have it installed or is it only a thing we use only once in a while.
Cheers
JP