Suppose only Fords have ignition-activated trailer charging.
All other brands might discharge vehicle battery without additional protection.
When constant duty solenoid -activated by ignition can be the cheapest DIY solution, you can buy battery combiner, what is solenoid with electronic circuit that sense the voltage on both sides and disconnect the power when voltage drops below charging voltage.
Advantage of it is - that it will keep your vehicle battery topped off when on shore power.
Insulators do have too many negatives to consider them in computer era.