Ok, so I measured the truck at a dealership. It's about 23-24" from the ground to the top of the reciever. Oddly enough a friends 1/2 ton tundra was about the same!

The boat people said that 18" is about ideal. I think they mean the ball mount, not the top of the ball. The goal is to fit the boat, but be able to adjust for other loads as they come along. I've already got more in drap bars

So in that case I'd be at the bottom of the adjustable 6" drop hitch, but still mid-range on the 10" one. The 10" one would be about 8" off the ground.

Am I doing the math right, does this seem right?

Chris, thanks so much for the help. But I'm getting 6" drop, you've got 1" drop, yet our target trailer heights aren't that far off...

 

To further the saga, the hitch on the ram is only 1" higher than that on our explorer. The explorer has a 4" drop on it, and the boat seems just fine. Of course the explorer sags a bit more than the dodge will. But both will probably sag some.

A 10" adjustable seems too big. The 6" it will be.