I intalled a new exhaust on my P150 last year. If you go to the thread titled "Jet size" there are a couple of pictures there. The exhaust bolts do not require you to take off any body panels, but you will have to lay on the ground a bit. They are a standard size (10mm I think) but are pretty long. One tip, there is a metal gasket that is part of the system, make sure you get that and if it is not damaged, you can use it for the new exhaust.
Smoke Eater