[87Skier]

You don't need a charcoal canister, but you do need a system of venting the fuel tank. Not sure how this was done on yours. I'm really leaning towards heat soak as well, just a little unsure of where it is happening.

Not sure if you still want a few pictures of what is going on at the back of the Blazer but here are a few:

The first is the tank. If it is a factory tank (or repro) it should have a vent tube on each side. Along with the fuel pickup, fill tube, and fill tube vent.

The picture of the back of the blazer is the vent tube. Note that my filler neck has been removed, and there is no cover in place.

Under the truck you should find 2 hard lines that run to the engine compartment. It runs along with the brake line. On the fuel line itself there is no rubber connections (unless yours has been modified), and has one hard connection near the front axle.

The other fuel line is for the vent/vapor canister system. It has three sections of rubber (not sure if that is common). The vapor system is not necessary but may reduce the gas smell at times, and could marginally improve fuel economy.

The last two pictures are the tank vent lines. These run to the tank vents and then back to the canister.