Yes, gas pipes will burn silicone wrap material. Ceramic coated pipes will help. Some guys have gone as far as using header wrap, but that's nasty stuff to deal with.
Just ensure you have enough ventilation and may be coat the inside of boat with aluminum tape to reflect the heat. Usually yu are ok if you have half an inch between pipe and side walls / deck. The bottom is not very critical as it is water cooled.
"The bottom is not very critical as it is water cooled."
I would disagree with this; the bottom is cool from the water outside, but the inside bottom can get hot from the pipe. Perfect senerio for bottom warpage which is the last surface you want going out of true. Use the foil tape on the inside bottom as well.