Interesting loophole that's worked for me. I'm actually crazy.
I've done a 6 month road trip around the country...all in my Samurai.
I did what you were saying hit the showers at Truck stops, hostels and what not. But i'd do combo sleeping 1/2 in Sammy - 1/2 in campgrounds. If i got somewhere and there was a campground i'd do it. If i got tired and was out in the middle of nowhere i'd get off the highway off ramp, then get on the same highway's on-ramp and park there to nap.
Usually truckers do this too, so your pretty safe since you'll usually come up on 3 or more trucks doing the same thing. No hassels from the local PD, or weird looks from people looking at you sleeping in your car. The 4-door is a dream for this. Take off the head rest and push the frnt seat as far forward as it go, then recline the seat back and it lines up with the back seat almost perfectly. Throw a sleeping bag over it or a puffy blanket and it's a bed! Also use some of that $4000 in travel cash and i'd seriously invest in limo tint for the back half of the truck. and a medium depth tint for the 2 front windows. This will keep the contents of the back of your truck from being cased by prying eyes. And the entire cabin of your truck a lot cooler.
The best part is with your windows tinted that dark, all you need to do is throw up a good pair of sun screens in the front window and you have privacy at night.
The trick with campgrounds that never ceases to amaze me. Is you can actually sleep there for free.
That's right. Free.
most campgrounds registeration booths close about 9 to 10pm. Pull in around 10, check to see when they open, pitch your tent and sleep till about an hour before the office/booth opens and hit the road.
You pay nothing and get a full nights sleep...not in your car. And if your lucky you end up in a campground that has a shower in it...an extra bonus. It's a great trick if you get low on funds...or on a tight budget. If you plan to stay a awhile then by all means pay for your lot...but if you just need a place to crash over night it's the best way to go.
Make sure your fuel filter is brand new and your rig is fully tuned up before you hit the road.