Areas that rust - Rear chassis
The capping plates on the main rear chassis sections are on the bottom, the formed sections being quite heavy top-hats with a thinner filler spot-welded across the flanges underneath (these chassis legs are cantilevered and stepped-up aft of the main floor chassis members, as they exit behind the rear cross-member)/
If water continually gets into these sections, the capping plate will eventually rust, the water can also get trapped betweeb the flanges and the spot-welds.
One way that water can get in there can be seen here Snorkel box, through the o/s snorkel box (on 2.1 Syncros, anyway) behind the o/s tail-light. (Drilling a 1/4" bang in the middle of the snorkel box floor, where the pressed fingers cross, can alleviate most of the problem I imagine. Deburr & swage it downwards a bit; helps stop water penetrating from below as well as draining properly.