Yes, aluminum foil may help out at least sort term. Old Chryslers are known for this.

Another thing you might want to check is if you are getting ANY restriction on the input side. If so the sucking of the pump will lower the pressure of the fuel. As you probably know lowering the pressure of a liquid causes it to boil at a much lower temperature. Another reason why most cars have in-tank fuel pumps.

Another possibility is that your pump is going bad. It may be generating its own heat and causing the gas to boil internally.

You might temporarily run a rubber fuel line from the inlet on the fuel pump to a gas can sitting in the bus (make sure it's not going to fall over) and then go for a ride on a hot day. That will at least rule out the input system.

For drag race cars they make something called a "cool can." You put ice in it to lower the fuel temperature so you get a denser air/fuel mixture. It's not necessarily anything you want to deal with but thought I'd bring it up.

Also gas is formulated differently for winter and summer driving. You may have some “cold Alaska gas” in the tank and that may contribute to its easier boiling point.