A quick update. And many thanks for the information those of you with constructive responses provided.
Turns out the water heater in my 2016 V3305 is an Atwood, so it has an aluminum tank and no anode. So that makes sense. I wound up cleaning it out using the vinegar cleanout process and after running a few tank fulls through, it's all cleaned out and the sulphur smell is gone.
I also did the bleach cleanout on the main water tank for good measure and it's all cleaned out now as well. I don't know why the water heater tank started to stink of sulphur, but at least the online tutorials I found for the anode replacement helped me zero in on the water heater, so all in all, I got the result I needed.
For anyone interested in why my local RV service guy thought the anode might be the source of the problem (with no manufacturer info to work from, BTW), the following link may give you some perspective. Apparently its a common result of a worn out anode in a steel tank or an aluminum tank. https://kleentank.com/oh-that-smell/