A quick google search turned up
this. I have no idea of the quality or whether the included bulb bases would work with your fixtures (though probably not), but it's a reasonable starting point and the price is reasonable and there are a bunch of related product variants to look into.
Another possibility might be the Ikea Dioder multicolor light pucks. I believe they use a 12V transformer (well, little switching power supply) to power them, so a bit of surgery should allow them to work directly from the RV's 12V system. Lifespan may be reduced somewhat by the somewhat higher than nominal 12V voltages often present in an RV.