Do these jacks stay stable on gravel or soft ground?

The polyurethane pads bite into loose surfaces better than bare metal. For very soft ground, dig out a small flat spot first and place a plywood square under the pads to distribute weight.

Can I use both jacks at the same time to level my RV?

Yes — that's the design. Use them on opposite sides or corner points depending on how your RV sits. Each jack carries 5000 lbs, so verify your RV's weight and distribute accordingly.

What do I need to do before storing these for winter?

Wipe down the metal and pads to remove dirt and moisture. Store them dry in a garage or covered space. The polyurethane pads don't need special treatment, but keeping them clean extends life.