12V LED bulbs with this E27 threaded base AND with a nice frosted globe will be expensive.
You may consider changing the base.
Or get
These CREE for $2.60 a piece. It won't be looking the same, with array of small lighting dots rather than one shiny globe. These "cob bulbs" have most of the light emitted to the sides, only a few light diodes are on the tip of the cob.
The equivalent brightness to your 20W old bulb would be 27*5050 SMD. Pay attention to color temperature.
Maybe you'll find them with frosted cover - I honestly didn't look, this link was the first I found, your fixtures are not very common in RV.