I still like the idea of a french drain around the perimeter. That should remove most of the water in the nearby soils. Gravel under the slab is probably almost a must as well. 4 - 6 inches of compacted gravel - tamped, will allow any excess water to escape from underneath the oven without developing soil erosion that could cause voids under the oven.
CJim - I'm wingin' it here. You know the answer? (yes!
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