Wow, this thead just got really complicated for a simple question. Let's assume for all of my previous posts the trailer was balanced correctly (weight on the tounge of the tow vehicle). With a longer distance between the hitch and the axel the trailer will track behind the tow vehicle better.

Since most of us trail with bows forward cat trailer have this "advatage" built in.

I would say that the chagne in weight of fuel in a tow vehicle is not going to make it unstable. It's not like we are flying in a small airplace with a fuel tank aft of the rear baggage compatement that when the fuel is burned completly changes the handling of the airplane.

As far as tire size goes, 8" tires will work fine. I like the larger tires because I feel better with that extra margin given by reduction in angular velocity of the bearings. I also really like the larger tire diameter for handling bumps in the road.