I thought more folks were concerned with bending the frames, rather than mere rust. That's why so many make those frame box kits.. http://www.ballisticfabrication.com/...es_p_1820.html
Knowing you Dave I bet you'd be happiest just pulling the bed off for a couple weeks, so you can get a 360 view of the frame. You're welcome to borrow my bug zapper for a while if you want to get crazy and box it in..
82 fj40, 99 uzj100, 06 gx470
05 525EXC, 01 XT225, 07 TTR90, 07 CRF50