[roadtrp204]

Go crazy with an awl or ice pick and poke at everything under the car. (Lower rear of front inner fender wells, lower side of side jack ports, rear bend in the logitudes, reinforcement on underside of pan for pedal cluster, inner bend of rear logitudes, right rear suspention mount, and rear half of the rear trunk come to mind.)Try to jack up the car using the factory jack ports on the sides of the rockers. The rear half of the rear truck floor in another place to look. My rear passenger floor rusted out in my possession and I live in the dessert! Rain water came in through a bad window seal and sat under the carpet for a year or so but it was limited to just the rear half of the passenger floor. Replacement was a not bad, about a 3 out of 10 on the difficulty scale. Cleaning the rust for a clean weld was where all the work was at, mig welders hate rust and are not to fond of chemically converted rust (save that for after the welding is done).

Side note: out of the three mig welders I use, Miller, Dent Fix, and Lincoln, the Lincoln weldpac 100 with the gas kit has proven the most capable at welding thin sheet metal with light amounts of rust on it.