We're going both tent camping and truck camping with our 200 this summer. I've done a good bit of truck camping in a 4Runner - treasured memories which are some of my life's favorite.
Roof-top tents are in high demand so there are no bargains to be found now. Plus, I'm sure many of them are on back-order. I think it's wise that if anyone is going to get a roof-mount tent to be very sure it's how they want to sleep. I recommend you take out the 3rd row - one of the easiest "mods" to do. After you pull the plastic pieces then the seats unbolt and come out quickly.
It's easy to make space in your rig to sleep. Take out the 3rd row, move up the 2nd, then put down pads/blankets/pillows and try it out at your home. Give yourself an afternoon to try different things including where you are going to store the food cooler/boxes, water, cold gear, etc. One huge advantage of sleeping in your rig instead of a tent is the ability to warm up quickly if it's cold. I've slept below 0F in my 4Runner and quickly learned my cold tolerance (which is more like 40F). Plus, as others have indicated, if it's going to be very windy then inside is preferred.
As long as you have enough sleeping and wearable gear for cold weather, enough food/water/toiletries, then there's not much more you need. It's really enjoyable to find a spot, sleep in the back, and then easily move on the next morning if so desired.
If you're wanting to find one spot for several days and roam around while you are there, put a tent to "reserve" your spot for the night.
You might want to look into cheap netting with rubber-coated magnets. These are used to allow a window to be slightly down for air flow and preventing mosquitos from entering.
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