I have a 2008 stingray 240 cs with a 5.0 volvo IO with 230 hours. I purchased the boat last year and notice a gas or petroleum smell in the cabin when it is closed up for more than a half hour. I noticed a smell of such coming thru the cabin floor drain which lead to the bilge. I cleaned the bilge with over the counter products 3 times. No difference. I had 2 marinas look at it. One stated the gas tank hoses may need to be replaced. The second stated stingray has no over the side gas tank vent. The gas system vents directly under the gas fill and may be drifting back into the bilge. No visible leaks were found If you run the bilge blower it goes away but returns in approx 30 45 minutes after you shut it off. If you put your nose close to the gas fill you smell gas even even its capped. The air inlet to the bilge is about a foot away from the gas fill. All the lines and pumps were checked. Any suggestions as to what may be the cause.