First - RV trailer frames are not "high quality" steel. Mostly just hot rolled, low carbon junk!
Look at most any trailer and you will see where the manufacturer has used sell drilling/self tapping screws to mount all kinds of things like the propane lines, underbelly, etc. I would bet a good dinner that Lippert has not done any type of stress analysis on this fastening method.
You will find the steel drills easily unless you try to drill very near a weld that has locally hardened the steel.