here's what i made. The front boxes are a tad larger then the rears, so that the rears fit inside them when not in use.
basically not any different then what you can do with wood.
You can actually work on the suspension, if you locate the boxes on 3 points; for work on front suspension i set both rear wheels on the box + in the front one box under the crossmember. It is stable enough when the boxes (steel/wood) are at least 2 feet wide. I have no concern about it tipping over whatsoever. And my 6 year old climbs into the car like it's a playground...
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and here's one located under the rear diff:
additional pic showing to have them laser leveled, as i wanted to weld the sills in with the car having it's mass on it's wheels. I hope this way i get better door shut lines when i'm all done.
You also see the small car lift that i have; it folds neatly flat when not i use so i can just park on top of it. But big disadvantage of it is that it a has thick massive beam running front to back; which is really close to the car when you lift it, making it impossible to work on gearbox , exhaust, guibo / drive shaft.