If you get at least 1 of the mount bolts into the metal frame work of the rv, it will work reasonably well, ........maybe a little directional if mount is on one side.
Rich
'01 31' Rexall Vision, Generac 5.5k, 1000 watt Honda, PD 9245 conv, 300 watts Solar, 150 watt inv, 2 Cos 6v batts, ammeters, led voltmeters all over the place, KD/sat, 2 Oly Cat heaters w/ ox, and towing a 2012 Liberty, Lowe bass boat, or a Kawi Mule.
Doesn't really matter who does or doesn't use it.. The OP asked a reasonable question. There are antennas that require a ground plane in order to archive a good match and decent radiation, and there are others that perform well (not great) without a ground plane. A lot of truckstop CB shop guys have been doing this since the 70's and know what works where and can either show you loaded ground-plane less antennas, or sell you metal tape to build your own ground plane on the roof. The problem is finding one...
If you want a mediocre to flat poor performance, just hang anything up there.