I think many off-road trailers are constructed with a steel tube frame and aluminum panels. But there's no reason why an all aluminum trailer couldn't be as strong.
I'd like to know more about the trailer's axle and suspension. Because these details are not described on the web site (at least I didn't see it) I'm guessing that the trailers have a conventional axle with leaf springs. More sophisticated designs use independent trailing arms, sometimes with air bags to supplement a coil spring.
I'd want to know more about the trailer's warranty. And I'd check to see how well the compartments are sealed against penetration by dust and water.
You might want to compare the Pacmule with designs from USA companies Adventure Trailers (
http://www.adventuretrailers.com) and Campa USA (
http://www.campausa.com). Also see Australian manufacturers like Kimberley Kampers (
http://www.kimberleykampers.com/) for ideas about how a proven off-road camper is built.