I will respectfully disagree with the last poster. I don't think it's strange at all. In fact, I have basically the same set up on my truck and TC. When parked at a camp ground frequent opening of the truck doors triggers the dome lights. Do does using the truck's radio or in my case ham radios that were wired to the truck. I liked the fact that my camper converter or solar panels were keeping my starting batteries topped off.
The camper can't drain the starting battery as you fear. When the voltage gets below around 13 volts the voltage sensing relay disconnects the batteries.
My starting batteries and RV batteries were both flooded lead acid, same chemistry. While technically not an ideal combination to charge in parallel the charging requirements are basically the same. I had no problems in many years.