That's where I used to have mine but out in the airflow:
Original stanadyne.
Still died on me.
I've got a few ideas why, but I won't speculate here.
Just for reference, I wouldn't be getting "muddy" swapping out on the road. I can crouch, reach in, disconnect the connector and plug in another PMD with out ever laying down.
Except after ricocheting off the bumper and the tooth going flying, you break your wrist when your body weight tries to yank it back out the nostril as you head for the pavement!
Mine didn't even have holes for a plate bracket. I had to drill 'em myself and make a bracket for the plate ('cause I'm too cheap to pay a dealer for one, and the local pick-a-part didn't have any).