It's been a while, but I... don't think that's how vapor pressure works? Pressures of gases just add together to make a total "air pressure"--each gas has its own "partial pressure", which is completely independent of all other gases it's mixed with. The vapor pressure of gasoline is just the pressure of the gasoline vapor itself when the gasoline liquid and gas reach equilibrium (vapor condensing and liquid evaporating at the same rate). So increasing air pressure shouldn't actually change the amount of gasoline that evaporates from the liquid fuel--only volume and temperature will affect that. When the temp goes up, the vapor pressure goes up. And with more volume, there's more vapor at the same temperature.

The first patent result I got for searching on vapor pressure and gas tank was basically adding an air-pressurized bladder in the tank above the liquid gasoline, which inflates with air as the pressure drops (less liquid gasoline, more volume for gasoline vapor), thereby taking up more volume to reduce the amount of gasoline vapor in the tank.

Admittedly I don't know quite what the TCH is doing, but far as I know this is how vapor pressure works.