@drewkaree I totally see your point and understand your perspective. There's LOTS of people who don't have a clue or respect for someone towing or just large trucks in general. Most 18 wheeler accidents are caused by the driver trying to avoid the vehicle that suddenly cuts in front of them because they're more important and in a hurry. I have people cut in front of me or turn in front of me while I'm towing our 5th wheel and all I can do is hit my brakes and lay on the horn. I'll even give them the finger if I have a chance!
Most modern diesel pickups in the 3/4 and 1 ton class have an engine brake from the factory. Mine is an '08 with the 6.7 Cummins and it does and works well. Travel trailers all have electric brakes and are controlled by a brake controller in the cab of the truck.
@B0at1n has a newer Ford, like all newer trucks then mine, has the controller built in. Most standard boat trailers have surge brakes that don't need a controller to operate.
Everyone of us on this board have some trailering experience because we all own a trailerable boat. Some of us are way more comfortable with the act of towing then others. I've owned and towed a trailer since '06 when we got our first camper in the spring and our Yamaha at the end of July that same year. The very first time towing anything of any size was towing our new to us camper home in the dark. I was a nervous wreck! Now towing anything is second nature to me and it's all recreational. I'm very comfortable and confident towing because I know my rig. If my rig was close to the legal limit to be able to tow double I would have at least tried it once. But as I stated before the frame of my 5er is not the most robust. It groans and creaks when lowering the pin weight onto the hitch in the truck. Our trailer also doesn't have a hitch on the back like B0a1n has. I have a square steel bumper back there. The Grand Design of the OP is a very well built rig. The only negative, and it's very small, is the tongue weight of the boat on the back of the 5er lessening the pin weight on the back of the truck. For as light as the 190 is compared to the camper I see no negative effects in the handling department.
For a fuel mileage comparison I average around 12mpg towing our 5er and I have a 34 gallon tank. I too, when towing, like to be looking for my next fuel stop at a half a tank. I've never calculated what I get when towing the boat, but I know it's not much different then running empty. It may actually be better at times because towing makes me keep my speed in check.