I'm sure Lockheed wishes it's rhino beetle could land just about anywhere, like the insect, but hot and powerful exhaust may preclude that capability except on specially prepared surfaces.
According to an article in the October issue of DTI (Defense Technology International), statements from Lockheed and the Navy conflicted with Navy documents about the temperature of the exhaust. Statements that the cruise/lift nozzle exhaust was "18 degrees hotter than a Harrier", and "...the difference between the F-35B main engine exhaust temperature and that of the AV-8B is very small" were at odds with a Navy document stating the nozzle temperature is 400 degrees hotter than that of a Harrier, and twice the typical Harrier ground temperature.
The difference alone (400 degrees fahrenheit) is just perfect to bake a pizza. Naval Facilities Engineering Command documents expect a 50% probability of standard airfield concrete "spalling" on the first vertical landing. (Spalling is a fancy term for exploding)
So much for "austere/improvised surfaces" as landing fields.