Hello!
When I was about your age, my girlfriend and I (who is now my wife of 35 years), took a three month road trip through 35 states, in a '67 VW Bug. I'd removed the rear seat and installed a carpeted platform in its place, about seat height, and we kept our gear stowed underneath it. When we camped, we stayed in campgrounds, and we mostly used a tent. On nights that were threatening rain, or when we got to the campground late and setting up the tent was too much trouble? I would remove the front passenger seat, set it beside the car under a tarp, and I'd shove the driver's seat as far forward as possible. I had a second section of platform, L-shaped, that had folding legs so I could stow it out of the way when not in use. That front piece bolted to the back piece, creating a much larger platform that was seven feet from front to back on the right side of the car, and a little shorter on the left. By sort of spooning together, we were both able to sleep quite comfortably in that dinky little Volkswagen. (Oh, to be that young again)!
BUT! That was then, and this is now, and you don't drive a VW Bug, so my personal best advice would be to consider a compromise between tent and car sleeping, and to stick with campgrounds, either public or private, rather than truck stops. I won't recommend a product by name, but there are tents you can buy that literally hook on to the back end of your car with an elasticized boot. They make large models for SUV's like my Jeep Cherokee (Photo attached), and smaller ones for small SUV's and hatchbacks. With the tent attached you can leave the hatchback or tailgate open (just be sure to switch off your interior lights to avoid draining your battery). The back end of your car becomes an upper berth, so you sleep up off the ground, while your stuff goes in the tent, safe from the weather. Alternatively, you can leave your gear in the car, no need to unpack or rearrange, and you can roll out your sleeping bag in the tent (hint: get a good air mattress). It's all one big space, so you have easy access to everything. There's good cross ventilation, and zippered mosquito netting panels that keep out the bloodthirsty swarms. You can stand up in it, no problem, making it much easier to change your clothes and whatnot, and with the rain fly in place you have privacy. I used this set up on a two month road trip to Alaska and back last summer, and it worked great. I was solo most of the time. The larger tent was a little bit tricky for one person to set up alone, but I figured out a system (Duct tape was involved, substituting for the extra set of hands that would have come in, um, handy). The smaller tents should be easier to manage. And in campgrounds? There's nearly always someone around to lend a hand with such things, if you need it. (Even so, always carry duct tape :-). And, honestly, you should try to avoid campgrounds where there is nobody else around.
I've slept overnight in many different kinds of vehicles, in all sorts places and all sorts of weather. Relatively speaking, the tent set-up I've described was like a palace by comparison, and resolves, or at least softens most of the concerns that Lifey raised in her reply to you.
Good luck, have fun, be careful
Rick
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