If that is a park model, it could be using the bi-metal thermostat that is quite different than the standard Dometic thermostats- often people mess with the anticipator, setting it too high, which burns it up.
If it is the bi-metal model, it can be replaced with a standard thermostat, but the wiring is different than any of the guides that have been published.
$400 could be outrageous, or it could be fair- depends on what all they replaced. It is outrageous that it failed so soon.
-- Chris Bryant