For what it's worth, here's my experience with Progressive, in Michigan.
I purchased my van (2016 Ford Transit) new in 2017. I added it to my progressive personal auto policy, replacing the mini van I owned previously.
Two years later, after converting and moving in to the van, I called Progressive just to make sure my camping equipment was covered, that there were no problems being a full time traveler, etc. When i described my set up ( water jugs, camp stove, sleeping platform) I learned that carrying cooking equipment was a violation of my auto policy. But based on my description, the customer service representative suggested RV insurance. I was transferred to another department, answered a few questions, and within minutes i had a full-time RV policy at half the cost of my auto policy. My title and registration haven't changed.
There were a few stipulations, like I can't use the van for business or to commute to work. The policy includes theft of contents (excluding my ebike) and liability, so I was able to drop my renters insurance.
I have no idea why it was so easy. I asked about doing the same with a conversion van I had, and was told it couldn't be done as it "wasn't the original purpose" of the vehicle .