A simple google for sliding cabinet shelf will find a lot of options. I'm not promoting HomeDepot over any other source but you can find examples HERE
. If none fit, consider disassembling one and cutting down the width.
In your case it's probably a good choice but be aware you'll lose a percentage of the width of the cabinet to the clearance required by the hardware. Unless you have European-style cabinets (I've never seen them on RVs) the face frame is narrower than the cabinet itself. Plus, the interior dimension of whatever shelf you install will be smaller still. If you fit it right you can maximize the available space but there will still be some loss. That might be exceeded by the space gained at the back of the cabinet that you otherwise wouldn't use.
Be sure to secure it from rolling out during RV movement. The cabinet door latch might do that but also might not be designed to resist the pressure of a rolling shelf.