I bought a topper for our GMC when we pull our TT. Not the first time I've had this set up. For us, this is why we have a topper: the kids toys, bikes, sometimes a generator and water jugs for boondocking, and the dog in a crate when we drive (yes, windows provide air!).
We can lock stuff up at night.
Additionally, there are many times we buy "junk" (read: antiques) and need a place to put it until we get home, again, to lock it up and keep out the weather.
Bottom line: For us, the ideal set up is having a topper. I even installed an LED strip light with a toggle switch. Man, its bright at night....works great.