As a corrosion technologist, I can speak to the hot water tanks. The reason they have mostly consistent shelf life is the heat, which is one of the 4 factors directing controlling corrosion rate. In addition to this the temperature also contributes to hydrogen embrittlement, this causes the metal to become brittle over time as it is constantly heated, eventually cracking, causing failure.
An aluminum fuel tank is actually quite well protected from corrosion internally as long as you don't let water accumulate and sit too much. Your main concern is going to be galvanic corrosion, dissimilar metals in contact such as screws/bolts. Outside of the tank is another story though, here you are more likely to have the tank in contact with a soggy electrolyte, such as wet wood, possibly salty, which can cause external corrosion. However, this corrosion will be plainly visible to inspection.
The short answer is no, there isn't a definite shelf life as long as you control corrosion of the inside of the tank, the outside of the tank, and wherever other metals contact it.