Any TT or MH roof structure is going to be "bouncy" compared to the
underframe of the same, so compressor vibration is going to resonate much
more from a roof mount unit than from a floor or underfloor mounted unit,
other factors being similar.
There are window mount (house) A/C and heat pump units that can be
adapted to RV use. It can even be done without messing up the appearance
of the RV like sticking them through a window does. Ducting would require
some ingenuity, though.
Al