Here's how I did mine, which worked great with my old camper. (was a bit short for my current one, so I had to redo)Beers have been involved, WATTS.
Yes, 2.5" receiver... I'll see about building one.
I bought a Curt receiver tube like this:
A trailer wire extension like this: (you can get them in several lengths)
Then some 1/8" steel for the wire, and 1/4" steel for the safety chain loopy thing. Drilled a hole for the pin into the truck, and with the shorter version that was it. When I extended it, I added the chains and turnbuckles since it's getting pretty long now.