I have a 20', twin 5k axle Haulmark: was a deal that found me. Was not even considering an enclosed. Even though I agree that 24' is ideal, having worked with this 20' for two+ years I would suggest to not rule out this size if a deal were to present itself.

Primarily I haul C3/C4 Corvettes (1968-96) in it, but have done B and E Bodies too. With the Vettes, space is of no concern even with a winch set up in the nose. The E body is very livable, the B Body is tight but not the end of the world.

My suggestions beyond ones previously mentioned: I'd recommend an arched roof and bowed nose unit. The arched roof is a must if it snows where you are: flat roof will not allow the snow to "flow off". It will sit there- then will just hold water and corrode the roof. The bowed nose will give a slight bit more room. The flat roof/flat front units are cheaper. Hallmark and the like (more $$) are arched. Look for torsion bar 5k axles, not the leaf spring 3.5k ones.