When setting your front to rear level, use the kitchen counter, rather than the floor. After all, the refrigerator is mounted there.
That said, perfectly level isn't really desirable either. You will want a slight tilt fore/aft and side to side to allow condensation from the air conditioner and water from rain, etc. to run off where you want it to run off. Allowing the water to puddle, especially around the AC is not good. I normally set mine to run off at the back right corner. This keeps it away from my pass through storage doors and my awning and doors.
By the same token, when you have your awning out, be sure to tilt it so that water runs off at one end or the other. Do not allow it to collect on the awning. This can be very expensive.