I had to put my through-hull in a spot where I have vinyl on the outside - I removed a circle big enough to give me a half-inch clearance from the fitting, but I wonder if I should remove more.
Because of the limited clearances I had to work with I wrapped a crazy amount of fiberglass insulating header wrap around the exhaust pipe on its route to the through-hull. I've ran through two 50 foot by 1 inch and one 50 foot by 2 inch rolls of the stuff. Thats on top of the fiberglass "sock" it came with.
In spots I have 3/4" of insulation in the places where it got within an inch of anything (worried about the blistering zolatone and/or the aluminum conducting heat to where it shouldnt be.
I have a min of 2 inches clearance to anything burnable.
Man this has been a PITA install - I got fancy with my ductwork, combustion air, exhaust, and outdoor fresh air/indoor air mixer and bit off more of a project than I expected.