Keep in mind to that the trailer frame flexes. You can get it perfect level, then drop your stabilizer jacks and punch one down too tight and lift the corner slightly. That corner is going to throw off the leveling. Its never going to be perfect. In fact there was a thread recently about using stabilizer jacks to level the trailer. This is why that's a bad idea.
This is a case where close is good enough. I'd rather spend my time in front of the fire instead of worrying about perfect level.