This is the correct way to do it . . I"m will to bet, if you check with the manufactured home builder, there are "Specs" that require pier footings to support the loads of the home. I'd bet the specs will call where to locate piers and or monolithic slab type details. Your load of the home isn't spread out evenly on a floating slab. The edges for sure are load bearing points and should be thicker, as what the monolithic slab would show. It should also be insulated to keep the frost out and acting on the slab . . . . . . Doesn't take much more money to do it right and be problem free .  . . ..

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insulation (full).jpg (49KB - 106 downloads)