Seems every year the topic of Lady bug and Stink bug infestations come up.
We had problems with Stink bugs for a few years. I solved our problem by purchasing some Raid bug bombs (Dollar General - 4 to a package - cheap, found usually on an end-cap).
Clean out your camper of any open food. Remove pet dishes. Put all all eating and cooking utinsils.
Set one bug bomb in the rear of the camper, one in the front of the camper, and one in the middle of the camper. Set the last one in your pass-through bay area, and if you can, even open the back wall of your bay area.
Now, before setting the bombs off, turn on your AC, all your AC if you have more than one. Now, set off all 4 bombs at the same time and leave the camper for an hour.
What just happened? The bug bomb poison was sucked up into the air ducts in the ceiling and any open holes or seams in the ductwork just now let the bug bomb poison escape inside your ceiling cavity. It addition, it now penetrated all the little cracks and seams around your slide seals, any holes in the floor, and any open gaps, including windows that have gaps.
After an hour, the smell will be gone. Wipe down your counter tops, wash the top bed covering, and wipe off any surface you use regularly. Do not wash the floor, walls, windows, or anything else. You will immediately see millions of bugs drop to the floor and you'll be sweeping them up for 2 weeks following.
After 2 weeks, repeat one more time. This time, instead of running the AC's, turn on the furnace on high (regardless of temperature outside) and set of the next round of bug bombs. Now, the bug bomb poison will transfer through your heat ducts, again blowing the mist under the floor. Repeat the same clean up. After another couple days, you are free to mop the floor or anything else. The bug bomb poison has penetrated every nook and cranny in your camper and anywhere a bug can pass through will have to travel through the poison, killing it once it touches it.
You WILL be sweeping bugs for the next 6 months as they attempt to come in.
Why the 2 weeks? The first round kills the parent bugs. The second round kills the babies after they hatch out and before the mature and can reproduce. Thus killing everything.
Meanwhile, that bug bomb spray will not hurt anything, will not hurt you, your pets, or the camper, as long as you wipe down the areas you actually touch.
The second year, repeat again when the bugs start reappearing. Do the 2 week cycle and I promise you, you will NEVER, NEVER see bugs inside your camper again, unless you leave your door open and they fly in ... But... if they do ... they die!
Some folks are afraid to do this, thinking the bug bombs will blow up the trailer. FALSE! Myth Busters did an episode similar to this, and in order to cause an explosion in an enclosed space, it took something like 200,000 cans of bug spray to cause a reaction.