You can download a low clearance POI set from POI Factory. But, the 2797 won't route you around these low clearances; just give you a warning as you approach them. I run the Dezl 760 and downloaded this set of POI's and set the warning at 4 miles. I've only had the warning go off once and that was for a road that passed under the interstate I was traveling.
The POI Factory POI's for campgrounds is more inclusive than those on any gps I've used and I think you will find that the POI's are updated more frequently.