Due to the limit in car lengths, I basically have to "protolance" my own piggyback cars.  Instead of traditional 90 foot Trailer Train cars or 60 foot converted flat cars, I basically plan on using Microtrains 50' flat cars with a fifth wheel and wheel ladder applied.  These cars will be able to handle modern 40' and 45' trailers without looking awkward.  The shot below is of such a car that  I detailed back in the '80s, which I need to replace the fifth wheel, and re-do the ladder to accomodate a wider range of trailers.

 

I will try to model some prototypes down the line, if I can find some that will fit the car length limits.  But there are many projects ahead of it.