SJT,
A friend has a gyro wagon that they work locally. When they get privilege. They are assigned chalked off area of some size. It has limited exposure on the sales side and the front to back is limited often by terrain or the back side of the other row.
If this is your case too, just get the largest that you can count on placing. As said, longer is actually easier. (This is something I will confirm from years of dragging things about.)
I can also confirm that any solid trailer beats a quick cover of any kind - If you have the room to place it. This is a memory of some art fairs we did. Weather was always a test, but the time we had a hurricane/monsoon/tornado was memorable.
If you are often in tight spaces, look up the power trailer movers. There are several on the market. With one of these (remember it will be deductible) placing the unit could be very simple.
Good Luck Guy
Matt