exhaust fumes in that body almost certainly come from the back door [gate/hatch] not being well sealed, I think Steele Rubber products has the proper seals for the back end ..... and pipe[s] that exit straight out under the middle area of the bumper like that will be a problem regardless, should be over to the side and angled down/out, factory was under the rearmost quarters slightly ahead of the bumper ends
Bill
