Slowpoke,
The aft jacks do "appear" to be very low on most RV's, but if you get a straight edge and go from the bottom of the rear tire to the bottom of the rear bumper, I'm pretty sure you'll find that the jacks are just slightly above that line. I know what you mean about how it "looks like they will catch on any dip" and most of us are aware and try not to get into any "obvious situations" but if yours is like mine and most others, it's more an optical illusion that they hang down rather than a problem on the road.
Check it out, hopefully you'll find they're above that straight edge line.
Oh, and the easiest way to get that line is to back over a piece of string and then pull it tight up against the bottom of the bumper.