Since you are dealing with gasoline you obviously need to be careful. Some fumes may be the result of refueling vapors. As you probably know gas is heavier than air and will seek the lowest level. Depending on where your tank is located in the boat, the size of the leak, if any, and the ability of any leaked gas to get to the stern would have to be evaluated, but per Chad's remark, getting the bow as high as is practical on your trailer would/might get liquid to flow to the stern, if a leak and bad enough to generate a reasonable amount of liquid. But to me a leak of that size would permeate the whole boat including the engine compartment.
It doesn't take but a smidgen of gas to make fumes that are detectable with the human nose. If you had a source that was anything to be concerned about you would have a nose full.
I'm sure you always turn on the blower on your bilge vent prior to starting your engine to clean out any fumes that may have collected there and it runs while the engine is running.
On an 89 year model, a leak in the tank may or may not be of concern due to the material from which the tank is made and age of the tank. Steel marine tanks are usually "terne" plated (a tin coating on raw steel to protect it from corrosion) which eliminates corrosion as long as it is homogenius with no voids. Alum or plastic/glass are usually maintenance free.
Fuel lines on the other hand can deteriorate and a "weeping" fuel line, usually at a hose barb connection is not uncommon in older lines. Also the gasket around the fuel level sensor plate (on top of the tank) can also deteriorate; sometimes cure is as simple as snugging up the plate's mounting screws....don't overtighten as you can destroy the gasket, especially if it is cork. So you might see if you can access your tank and check these things out.
HTH,
Mark
