You can have a guest on board for measurements, all of the work is done at the shop of the canvas guy. For final fit, finish, and attachment, all can be done at a guest dock somewhere or if it's like my marina on Sunday when no one is there.
My 8.0 BTD started sooting a few years back, it turned out to be the exhaust mixing elbow. It was over 50% clogged with soot and needed to be replaced.