What most people forget is the rubber plugs on the body opposite the chassis beam under doors. I have a '98 Pajero and removed those plugs
and was feeling around with my finger inside the holes and found a thick layer of sand & grid. Perfect situation for rust to form! I then washed it out with a hosepipe and could not belive all the stuff that came outa there. FYI....
If you get under your vehicle on the doors side and look just opposite the chassis on your body itself, you'll find the rubber plugs (should be five of them). They are sometimes dirty and difficult to see. There is flood holes for water to run out, but believe me you'll still find sand in there! Just take a hose stuff itn the holes and wash dirt out until water that comes out clear. To make sure feel around with your finger. Can treat the inside with Tektol or oil, your choice.