We have a 2011 Sabre 31RETS fifth wheel, being a newbie I am not sure where to check for level. Should I check on the bottom of the pin box or is there a better place to use?
The floor, just inside the door opening for front to rear, will have to go inside for side to side. Get the floor level, that is how they are suppose to build them.
Like Windrider said, then after you get it level slap on some graduated levels near the front (or wherever your jack/landing gear controls are). Makes leveling the next time easier.