If you have any doubts; a carbon monoxide detector would be a really economical "piece of mind" investment, but most manufactures will not install a catalytic type heater for that reason alone. They should be installing one that draw it's combustion air from outside and exhausts to the outside as well.
That said last year or maybe two years ago now; when Trails West's (Production Manager?) was participating in the forum, I did not get the feeling that he really knew the necessary construction details. That I would demand to be taken, being a fabricator myself, to get me to ever buy one of their trailers.
That said, Your money-Your choice!