My driveway at the new place is on an angle and so was the old place.
-Old place: chain to carport (unfortunately downhill from where the trailer lived) and a log under the wheel, angled so that it would run into the fence/carport
-New place: if parked facing downhill, then it would have a chock/piece of wood to hold it. Currently parked across the slope though, but still chocked as there's a slope that way as well.
Personally I like it being on an angle, as I drop the nose down so that the water drains off the cover better - we had it on the levelling ramp and levelled off and the water pooled; pulled it off and dropped the nose, and now no water pools on the cover.