I would jack up the car and put it on axle stands, put on some overalls and a face mask and carefully clean the underneath of the car to get rid of all the crap on the underneath and then once it's dry simply put underseal on the parts that got scraped so they're protected from rusting.

Ran over a damn curb in a parking lot today ....was pulling out of a parking space and didnt realise it was on the passenger aside of the car....i turned as i pulled out and it went under the car from just behind the wheel arch to about midway down the car .....had to back off of it ....damn i felt dumb and very pissed ....not sure if damages is structural or just superficial .....first pics are of the drivers side last 3 are of the damage ....what do you guys think ????

See my photos of curb dmage at PhotoPoint