All you need is a 12V LED bulb that has dimmable diodes and a 12v device to dial voltage up or down. Avoid the tacky self contained battery stick on stuff, do you really want to go around and turn off 20 lights at bedtime?

So a bulb that fits the existing fixture, I would have to look at it to know which base is best but this has the right specs: https://www.amazon.com/Letaclanic-Lighting-Dimmable-Equivalent-Silicone/dp/B08K8BSJ8K That has the driver in the base of the bulb so you can just hook right up to the power source.

And then reroute the existing switch wires to one like this: https://www.amazon.com/Halogen-Incandescent-Dimming-Control-Lighting/dp/B089N9WYGT/

If you really wanted to you could leave them on the existing on/off switch and splice in the control box of a cheap set of dimmable rope lights for use with the remote. I wouldn't go this route with a dimmer switch though.

Not all LED's are dimmable, and you have to make sure everything is rated for 12V and not household. I doubt the RV mfgers are spending extra on dimmable LED's and then not selling that feature, but it never hurts to look up the model number on your existing bulbs first. But other than that, there is not a ton of work to converting your existing LED's to dimmable.

So maybe I'm not putting in the right search terms

Not sure why you're not seeing them. Maybe try "12V" instead of "12VDC", Anyway, here's one.

Why don't I use those, because those are already set for 110V?

Yes, that bulb and socket should work fine, and you could then use a wall dimmer. Personally, I try to minimize the amount of high-voltage wiring. But if everything is enclosed within the fixture or ceiling, you should be fine.

In your situation, the ground wire only needs to be connected to any exposed metal parts of the fixture, not to the bulbs. This is for safety, in case a "hot" 110V wire comes loose and touches the fixture housing. That prevents someone from being electrocuted, and it's the reason I don't like to use high-voltage bulbs.