I've done it both ways, just experimenting, and it doesn't seem to matter. Thor doesn't offer jacks on my RV, just stabilizers, so it makes sense that it should work whether or not it's totally level. I added the jacks later (Bigfoot). Usually I'll put the jacks down first. My slide is small and relatively lightweight.
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2021 Thor Four Winds 26B on Chevy 4500
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