trailer tongue length

Never heard of a 5th wheel hitch on a DP.....as stated above -- the longer tongue keeps you from hitting the back of the DP when turning.....My enclosed trailer is 32ft long with a standard tongue and I have an 8in extension on the ball insert. I have towed this set up since 1999 and so far never touched the trailer.....might be able to get away with regular tongue on an open trailer. I just came in and out of Cal (Pamona)at 70ft and never had a problem.....all the way to Orlando.

Use a 5th wheel hitch.

You need at least a 4.5' tongue to be able to make full turns with an 8.5' RV, and that's assuming mostly flat pavement.

Does California really measure though?

The tongue length seems to be more of an issue on enclosed trailers vs. flatbed trailers. It can still catch the rear of the coach lower on the rear end cap but up top is the bigger issue. If a standard tongue is used with an enclosed trailer, you are turning and going through a dip there is a very high chance of catching the top of the trailer on the top of the rear end cap of the coach.

This is the reason most, myself included, recommend getting an extended tongue when ordering an enclosed trailer. Many trailer manufacturers actually call them an "RV tongue".

Mike.

It is not the length of the tongue that becomes the issue, it is the distance between the ball and the axles.
The shorter tongue will effect turning radius of the combined rig. Your MH may turn sharp enough that the trailer will contact the rear of MH.
Length of trailer between ball and axles will change the tongue weight. You should try to calculate the center of the cargo and trailer to achieve a proper tongue weight for your hitch setup.