To hold it solid, and keep anybody from moving chocks I would get a pair of good rubber mud flaps for a truck, some nuts and all-thread and some short 4X4s. Bolt the board to 1 end of each flap. When parking, take trailer back past where you want it. Lay flaps in front of tires, pull onto flap and against block.
Note if the drive is steep, the rear might hit ground before the front is high enough to call "level" If that is the case build a pair of ramps with stop block on top, and rubber on bottom so pull on rubber before ramp.