We use blocks of memory foam... they're roughly 3" square and anywhere from 6" to 18" long. We place them on the front of the shelves and the closed doors holds them - and anything behind them - securely in place.
Best of all is that they're flexible so they'll contour around anything in your fridge, and you can always cut them to fit exactly where you need them.
The DIRTY ROTTEN RACKLEFRACK! 2004 Newmar Mountain Aire 4302
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