Holy crap, look at the big brain on Amoeba. Just use a stronger magnet! Er, let me explain.
As pointed out by Lessen and others in this thread, using a metal washer glued to the underside of the body risks ripping paint off if pulling the body up off the magnets on the posts. So instead, use the same setup (strong small disc magnets on flat-topped posts, washers glued to body underside) and use a stronger rare earth magnet as a pull handle. Place the stronger rare earth magnets on the ends of a two-pronged t-handle (or something similar) and use this "RCNT Mag-Pull" tool on outside of body over washers and pull the body off. This way there is no paint risk. The stronger EM field of the pull tool magnet grabs the washers with enough force to overcome the opposing grab from the post magnets. All the pulling force on the washer is then into the body lid and not away, negating any stress on the paint. You would want to align the post & Mag-Pull magnets in opposing poles so all force is on washer and not two rare earth magnets trying to mate through lexan
I'll order some 3.2lb and 8lb force neodymium disc magnets to test this out. I'll have to do some testing to find a sweet spot between lid holding force and release grip with the "RCNT Mag-Pull". You also want the body holding force to be strong enough to keep the lid on at WOT speeds but weak enough to pop off without pulling paint on impacts etc.
Assuming it works as I've calculated we may want to ping GH or one of the other fabricators lurking on RCNT about getting these made commercially. EEM's velcro body mounting system shows there is a demand for this kind of mount type so it could be a viable alternative solution and since most post mounts are standardized in distance between posts you limit the need for brand-specific makes.
You can get neodymium disc magnets with very small EM fields (1/16") which also goes a ways towards minimizing potential RF/EM interference though would have to look into the technical specs to ensure it's reasonably safe.
Idea dibs!