Toggle bolts through floor/metal, strapping to the ribs...
To make something completely fixed, needs to have anchoring point for all 3 axis.
For example, your fridge: you could strap it left-to-right and against the wall nice and tight (do i get brownie points for rhymes?), but if it has room on top, it could bounce around, and eventually pop loose.
Brackets, straps, even all-thread replacing wheel/mounts will help.
Does any of that make sense to you?