THe trick will then to be ........mount a underbelly pan that goes from the new lowered lip back at least 18-24 inches.
I have a lowered front bumper on my 02 infiniti Q45 and there was 2 inches of gap to the factory underpan. The new underpan with the lowered bumper helped significantly with the quest for mpg.
here is the gap created by the lowered bumper and the factory pan.
here is the custom pan the goes edge to edge and back 24 inches:
