[oil pan 4]

You could do something like a conveyer belt air dam. Just hold it on with like 4 or 6 bolts and pull them off and throw the air dam in the back.
The 2/3 air dam on my suburban was good for nearly 1mpg.

Why would you want mud tires?
They are expensive, lower your fuel mileage, wear out quickly and need to be replaced well before they are worn out if you want them to be useable off road.

I say run highway tires or A/Ts with bad ass snow chains off road.
Or get a spare set of mud tires.
You can throw nasty set of snow and ice chains on a bald high way tire and do things the most radically aggressive, expensive mud tire with full complement of tread can barely do.
Another thing is most mud tires kind of suck in the snow and ice, I would rather have A/T tires. Ideally anything with chains.
Chains protect the side wall and shoulder to some degree too, plus if you do cut the side wall on a highway tire, who cares, its a cheap high way tire. If you cut the side wall on the most radically aggressive, expensive mud tire that still has full complement of tread, well sucks to be you.