Where's a good place to buy a riser for my Class 2 trailer hitch? I need about a 6" riser I think. Thanks.

Trailer should be level when towing. You can buy them most anywhere. Any trailer  rental like UHaul, Wally World, Home Depot or other big box stores, online.

Try UHaul they have a special locking ball which will not come loose.

As someone mentioned, it should be as level as possible... however,  if you have to choose one or the other, you would rather it be with the hitch end of the trailer slightly lower than the other end.  This places more weight on the ball and helps reduce trailer sway.  As they said though, as level as possible. 

Thanks. So just find a level spot and put a level on the trailer frame?

Thanks. So just find a level spot and put a level on the trailer frame

Yeah that or you can eyeball it.  Just measure from the ground up to the tongue receiver and then measure the ground to a little above the middle of your hitch (because the ball sits on top of the middle of the hitch).  Subtract the two and that's the rise/drop you need.