i like to use extend on any rust work i do... it supposedly kills the rust then put the underbody stuff on... nice thing about extend is you can use it anywhere on the car... and paint over it ... never know it was there...
Flipping the car over isnt that big of deal... they make rotiseries to do that... or what i did... prolly not the safest way to do it.. but i build a cradel to hold it... and took a engine hoist ond hooked on with cross bars on the core support... and then put a rod in the gas tank hole... and picked up and spun it... then set it in the cradle... worked real well.. but prolly dangerous... but u also have to strip everything out of your car... motor
tranny and all...