Horrible MPG/Fuel odor troubleshoot

Way to rich on the carb along with openings or leaks in and around the trunk and rear end area is what it sounds like.

Exhaust all the way out the back?
Trunk seal?
Holes in the metal or body plugs missing?

The vacuum at the rear of the car from the car moving through the air WILL suck that exhaust into the cabin, and running way rich compounds the problem.
It would explain the mileage also.