LJAZ is correct... I was able to get the framing details for my '08 X210 WBS model. I couldn't get any other plans (I also wanted the wiring and plumbing layouts, but, they wouldn't release them. They, and most other manufacturers, don't want to release those due to inaccuracies; apparently those plans are "guides" only and aren't strictly adhered to...) You can give them a call and ask; they emailed them to me in pdf files.
Another "option" is to use one of the newer "sonar" stud finders. I have one that I use for home remodeling and it uses a "sonar" type finder to locate almost any density difference behind walls - studs, pipes, cables, voids, etc. I've used it on my new 5er (Keystone won't send me any plans at all) to locate some of the aluminum framing on it...I'm going to make my own map
As for "holding power", in case you can't find a stud or two... At most big box home stores (Lowe's, Home Depot, Ace, etc.) you can find hollow wall threaded anchors. These are usually a white/off-white thermo plastic with large threads (> 3/16") around a conical base. Virtually impossible to pull out, even in something as thin as the luan inside walls. A dab of 6000 sealant when you screw it into the luan and it becomes part of the wall. Unless you load your cabinet with 50 lbs of stuff, those should hold it up for the life of your trailer.