The biggest consideration to retrofitting Outback or Magnum inverters into a Vantare or a Parliament coach is that the existing 4000W Trace Units have two AC inputs. They synchronize with each AC source (either shore cord or generator), and actually operate in parallel with that source. There is NO "automatic transfer switch" in these coaches because the inverters ARE the transfer switch for each AC leg respectively.
The installation of Outback Inverters into a Marathon Coach would be a little easier, but there are still issues that keep that retrofit from being a "Plug-and-Play" situation.
There ARE still Trace SW4024MC2 inverters out there, or the other alternative, with which I will be experimenting in the coming months, the Victron Energy Quattros. These units have the same basic design idea as the SW-series Trace/Xantrex, but with up-to-date network capabilities, less user-interaction (aside from setting the Shore Cord size like the SW's), and Series AND/OR Parrallel-Stacking capability. I will write a formal evaluation of the use/operation as well as retrofit-ability as a replacement for the Trace SW-series as soon as I have completed my testing and evaluations.