I would be willing to bet a large sum of money that everything you listed had nothing to do with the fire. Could be something as simple as forgetting to turn the blower on.
While anything is possible incorrect work, using incorrect products or unsafe installations & not following code are
usually the cause of boat fires. That was my only point, not to guess the
actual cause...
But more likely a bad fuel line as a result of Ethanol in the gas, which has nothing to do with any codes. It is notorious for eating fuel lines and catching boats on fire.
A leaking fuel line does not catch a boat on fire unless something is there to ignite it. Any good gasoline boat installation would also have a gas leak detection system that is compliant with ABYC A-14. I can count on one hand the number of times I have seen an owner of a gas boat install such a system. On a gas boat everything should be IP rated to avoid spark yet I see non IP alternators, starters, over current protection, switches, battery chargers etc. etc. etc. installed inches from a gas system. Fuel lines should also be ABYC / USCG / SAE J1527 compliant & preferably A1-15 rated.. A1 or the newer A1-15 are extremely rare in my experience when fuel hoses have been replaced by boat owners. I have yet to see any
A1 or A1-15 compliant marine fuel hose get voided by gasoline / ethanol it is usually 20+ year old fuel lines that do not meet or even come close to today's standards.
Trust me, all the DIYers know about it, because those are the guys who spend time on the forums. Its the boat repair shops that I worry about.
I really do wish that were the case but I am aboard hundreds of vessels per year and it is absolutely not what I see. Compliance with gasoline, electrical, LP, seacocks & diesel fuel systems are rarely complied with, and it is downright scary. Any good boat repair shop will have an ABYC logo on the door or highly visible. Ask to see the ABYC certificates of the guy working on your boat. He has been trained to do stuff to the standard which will be far safer than guessing at what the standard may or may not be..
Bottom line is a boat with SAFE SYSTEMS should never have blown up.
#1 If gas or vapors had leaked the gas detection system would have alerted the owner to it.
#2 If the proper marine hose had been used, it does not rot through from ethanol.
#3 If the boat was properly wired, used proper IP rated equipment there would be NO SOURCE OF SPARK....
Every boat fire I have been involved with has been due to non compliant installations of either electrical, LP, or gasoline systems....