I think I would buy the tow bar and braking system and then put the RZR and kayak in the truck. I've towed a lot of trailers, but I wouldn't be too thrilled with the idea of the truck and RZR both on top of the trailer behind the MH. This assumes your truck can be towed four flat.
The advantage of putting everything on the trailer is you can buy and then have the trailer for probably the same cost as getting the truck ready to tow. And if you want to trade in the Dodge for a Ford or Chevy, (I'm sorry, but I couldn't resist that one) then you aren't going through the hassel outfitting another truck. I imagine the truck at about 5,500#, the RZR about 1,200#, the trailer about 2,000# and then throw in all of the other little stuff like the kayak, RZR fuel, fire wood, etc. and that puts you at at 9,000#.
If you have the RZR in the truck and the truck on a trailer, that's gong to be a PITA when you want to get the RZR out for a spin without unloading the truck also.
Bill
Nodwell RN110 out moose hunting. 4-53 Detroit, Clark 5 spd, 40" wide tracks, 10:00x20 tires, 16,000# capacity, 22,000# weight. You know the mud is getting deep when it's coming in the doors.