Motorhome built-in tanks have a gauge that actually shows how much propane is in the tank (with a float to measure the level), so it's not too hard to avoid running out. This is generally hooked up to the tank level panel inside, or you can peek outside at the pointer and see a much more precise reading than 1/3 - 2/3 - F from the little lights. Most motorhome tanks are also a good bit larger than a cylinder; mine has a usable capacity of around 60 pounds if memory serves.
Most RVs with dual cylinders have an automatic switchover regulator that will draw propane from one tank, and when it gets empty automatically swap to the other one, popping up a little flag or other indicator to show when that happens. You generally don't need to open and shut the cylinder valves to use them one at a time; just check the indicator as needed and refill the empty tank and switch a lever on the regulator so it can switch over to the just-refilled one once the other one is empty. It's much nicer than having to go out in the middle of a cold night.