A new NT30SP furnace is smaller than the NT22a, so you'll have to build it a platform to get it up to the height of the intake/exhaust ports in the skin of the trailer.
You can build the platform as a plenum to attach ducts to, but you'll likely have to modify the ends of the ducts somewhat to get it all hooked up.
They're not particularly cheap, but have a lot of nice advantages over the NT22a. They're rated for a lower amp draw for the fan motor, and they're spark ignition rather than a pilot light.
Zero Gravitas — 2017 Flying Cloud 26U | WBCCI# 15566
He has all of the virtues I dislike and none of the vices I admire. — Sir Winston Churchill