stick a hose in the chassis rail and turn it on full ball till u can stick ur finger in there and not find any sand (this may take a while)
then wait for it to dry and get a can of fish oil or lanolin oil (not crc/wd40) ant take the spray nozzle off bump it um against your chassis to push the end into the can and the fluid will spill out very fast shove it in your chassis rail (1 full can each side) no rust it a great place to start when your jeep has done alot of sand work.
then rip off the plastic bumpers