Nerfherderiam

By the way if you are really concerned about it, there are company's like Eastwood that sell gallons of salt neutralizing chemicals you can put in a spray bottle and liberally spray on your car. It counteracts the corrosive properties of salt. With a weed sprayer or similar you can spray it inside holes/openings you would like not likely be able to totally flush out.
 
 
 
 

I use APC in my foam cannon for pre-wash on cars that I'm detailing.  I think that would be your best bet.  If you have the snub-nose pressure washer handle, that would make it even easier to get under the car.
 
So I would:
Powerwash undercarriage
Foam undercarriage with APC (I use 4oz in the cannon and a little bit of car shampoo might make it cling a better)
Powerwash/foam the car and strip wash
Pull the wheels and deep clean them seperately
And then go ahead and do whatever cleaning/claying/polishing/protecting you think is necessary

Start with the foam cannon and ultra foam shampoo or regular shampoo (your choice) then wash the car using the two bucket method. After you wash the car and while it is still wet, grab your detail spray and clay. Spray down an area with detail spray and clay the panel, the move around and clay the car. After you clay you can wash again or just rinse off the car. Then while the car is still wet after the final rinse use h20 guard and gloss with two microfiber towels and wet one towel down. Next, spray h2p guard and gloss on the panel, use the wet towel to spread the product and your other dry towel to buff off. Then stand back and enjoy the shine!