Andrew the one I use which you know about is a Garmin 2595LM.
Its not an RV one but it still works for me.
I'm sure they have a newer model as mine is a few years old.
1. First figure what size screen you want 6", 7" or larger.
2. You said you want voice command and most Garmins have that.
3. Next you definitely want life time maps.
4. You also may want to consider the one that tell you about local traffic and accidents.
5. Price ranges from $249 and up. One of the new ones I looked at is the Garmin Nuvi 2799LMT which costs about $270
Here it is for $229 no tax and I think free shipping