If you have cash to spare and want a toy, go for it. Personally I would go to Walmart and spend around $8 on a set of stick on levels from the RV section. Using an old fashioned level on the counter or on the bottom of the fridge set the trailer up level. Then put your stick on levels on the side and front of the trailer. It won't take many trips before you know by looking at the level how many boards or wood blocks you need.
Another item that makes it really easy are Andersen Levelers. Place that front level where you can see it from the truck. Put the levelers behind (or in front of) the wheel and back up (or pull forward) until the bubble is centered.