I have stayed at Flying J twice in an emergency and one other time because it was convenient to the train station where I had to drop off my traveling friend at 3am. We arrived in the early evening to look over the safety factor of the truck stop, we ended up dining at their Denny's and staying in their lot until ready to depart for the train. Afterwards, I was able to return to the Flying J and sleep until I felt rested enough to drive. The closest campground was an hour away and the truck stop was only 10 minutes away, so it worked for me.
Park in the RV or car lot. Do not take up truck parking. Truckers are limited by strict laws the number of hours they can drive and need those spots for rest. An RV-er falls under no such laws.
On one occasion I believe the truckers became irate at an insensitive soul who pulled in with a 45 foot diesel pusher towing a big jeep. He then parked along the curb perpendicular to the truck spaces which made it quite difficult on the other truckers pulling in and out. The next morning, incredibly, the RV-er had 3 flat tires, 1 on the jeep, 2 on the RV. Such bad luck! The two parking lots were clearly separated by grass medians and well marked with signs. Read and obey.
On another occasion I saw a couple in a big RV ignore the car and RV lot sign, sail passed the truckers only sign, then park in their lot. Two truckers pulled in and each one parked about a foot or less from his rig on both sides. They couldn't even get out their door or see out their side windows. Their mirrors appeared to be an inch from the trucks. It pays to read the signs and obey.
Personally I feel like when I boondock at a business that yes, I should spend money at their establishment as a courtesy.
Those parking lots didn't go up for free.
The problem with Flying J was that when I went in their well stocked store, there was the aroma of fresh baked pizza, so doggy and I had pizza for dinner. The next morning I went in for juice and there was fresh baked sausage biscuits so the happy pooch and I had that. They also carry a ton of useful RV parts and just about anything made for 12 volt living. It would have been cheaper for me to pay camp rent, cook at home and not shop their store. ;D The puppy wanted to stay forever, he liked the good eats.
In one case the weather was disagreeable and I needed to run my generator. For $1 more I could have camped at the state park up the road, so there was no substantial savings. :
Check ahead, not all Pilots allow parking, though all the Flying J's do. I have been at Pilots that had a plethora of signs warning there was no parking or loitering or over nighting for RV's.
I try to plan my trips to take in campgrounds and slow down, rest, relax and enjoy. I know some folks are forced into driving back to back days because of their chaotic schedules, but whenever you can, take time to enjoy the journey. 8)
If you have chosen to boondock at a truck stop, you can't justify complaints about noisy truckers. It's the nature of the beast.
Campgrounds have quiet hours, pay for them and enjoy.