Whether or not gas is going to explode depends on whether or not it is between the upper and lower explosive limit, meaning you have to have the right ratio of fuel vapor to oxygen. Gasoline fuel tanks
accomplish this both by keeping the fuel vapor to oxygen ratio too rich and/or preventing a source of ignition. I don't think a honeycomb structure would have anything to do with this.
kept outside where the vapors cannot accumulate are considered relatively safe. Gasoline can be stored inside in a USCG approved gasoline tank that is also installed correctly but you must also have a blower for venting possible vapors.
Personally, I don't like seeing gasoline stored inside on larger boats. It is just too dangerous. Any gasoline I have to bring aboard the research
boat is always kept outside.