If your RV's wheel covers (sometimes called wheel simulators) (aka hubcaps) do not connect the wheel/rim via a nut or some other secure mechanism, then they connect via the shear force of the wheel cover's metal prongs pressing against the rim. If your wheel covers are connected simply by the pressure of the cover pressing against the rim, then YOU are just waiting for the wheel cover to disappear.
A RV rear wheel cover (concave) with a center hub attached to it (adding weight to the wheel cover) increases further the probability that the cover and hub come flying off). And you can spend $200 or more to get the missing parts replaced.
Here's a solution that uses stainless steel zip ties. Looks like a permanent fix to me.
https://www.bing.com/videos/search?q...FA&FORM=VRDGAR