I'm running a MK 70# PD unit on my 18'er and have had it out tolling in very snotty conditions, 3-4'ers with a close interval, (boat was basically a see-saw) and the TM handled it without issue. It's a 60" shaft TM and the motor kept planted in the water without it sucking air.
Not sure how an Ulterra would compare to a PD, but the motor, prop and shaft are the parts that take the pounding, and they are most likely very close (or the same) between the two...
My boat is a dual console aluminum and probably weights 3500# loaded. I don't troll with the TM going against the waves as that will eat up the batteries quickly, but it will hold it's own going into the waves when needed (reeling in a fish, clearing lines, etc.)