Here are a couple of tips.
Make it harder for them to steal anything, roll up your vehicle's windows and lock its doors.
Make your stuff less attractive to thieves, cover valuables with a blanket and don't flash expensive gear or jewelry.
Exude confidence, look people in the eye, walk with a confident stride, and make it clear that you are not someone to be messed with.
Being able to back up that confidence with pepper spray (if legal for you to possess) will also help your confidence.
Maintain situational awareness, are the other people families with children, fellow outdoors people, or do they give you a bad vibe?
Listen to your gut, if your hair is standing on end and your muscles are tense, leave the area immediately.
Finally, remember that your life is more valuable than your stuff
outdoors.stackexchange.com/users/8794/Charlie Brumbaugh
Caravan parks often have safes for people to use (rent).
That's likely your best bet.
They're often a bit like the lockers you get in swiming baths.
Baring that it's either hide things (Bottom of a sleeping bag works ok but obviously your taking a risk) or take anything valuable with you.
outdoors.stackexchange.com/users/None/
Camping is an outdoor sport, with many opportunities for unexpected events.
Don't bring anything that can't be exposed to the weather, and don't bring anything that will cause you emotional hardship if it does not return home with you.
I have been camping for years, and have never lost anything to theft, nor has anyone I know lost anything to theft.
I have had things destroyed by getting to close to the fire, ruined by water, worn out from over use, lost through misadventure, left behind accidentally, or otherwise made unavailable for future use by something stupid I have done. Apply some common sense and don't leave your wallet laying in the middle of the road.
But you need not be overly concerned about theft.
In the US there are two very general types of camping area, Private and Public.
the private places are run for profit and almost always have people who rent (or lease) the same spot for years.
The public ones are government operated and usually have a two week stay limit.
In both cases, there are people who spend their whole time in camp.
At any one time it would be unusual for there to be more then 2 out of 3 campsites having their occupants gone.
Everyone tends to keep an eye on what is going on around them.
Only a few bring a television and satellite dish.
Everyone knows who belongs to what campground, all of this makes for an environment that is not good for thieves to operate in.
On the other hand, a common occurrence is for someone to be away from their site and have a wind come up
that is greater then the wind resistance of their tent, canopy or other item.
The neighbors don't just watch your tent blow down the road, they go get it and take it back to your camp.
They may or may not put it back up and secure it better, but they will at least make sure it stays in your site.
outdoors.stackexchange.com/users/4079/James Jenkins
I just was told this last weekend: Lock your tent!
Of course thiefes can cut the tent and still steal your stuff but at least your insurance is going to pay if the tent was locked (check the conditions of your insurance and in doubt ask your insurer).
Besides that you should not leave your valuable stuff in the tent alone, also if it's just valuable for you like the knife your grandfather gave you years ago.
outdoors.stackexchange.com/users/2653/Wills
What I've learned in half-a-century of camping...
First, don't get too stressed out - in most developed countries theft is rare.
Don't let your concerns spoil your holiday!
(But be sensible - there are a few countries were camping would be risky, so do your research.)
Second, as far as you sensibly can, leave your valuables at home.
In particular don't take anything irreplaceable and of great sentimental value.
Third, carry critical documents (passport, insurance, tickets etc) in some kind of hidden under-clothes security wallet and keep them on you at all times Fourth, if you are car-camping, keep anything of value locked and unseen in the boot/trunk of your vehicle when you're away from your tent.
Alternatively, in an organised site there may be lockers available.
When I don't have a car, I prefer to carry my most expensive lightweight gear with me in my backpack when I'm off the site - my high-end sleeping quilt and mat, my camera and electronics, my down clothing etc.
It doesn't really weigh much, and it gives me some piece of mind.
Before you go off-site, tidy up your pitch, tuck everything out of sight and zip up your tent.
Make your site as anonymous and uninviting as possible.
If you get to know your neighbours and they seem trustworthy, ask them to keep an eye on your stuff.
It's really just a question of common-sense.
But above all - relax and have fun!
outdoors.stackexchange.com/users/5814/Tullochgorum
This summer. I will be camping on my own at a coastal caravan park located between 2 towns. In terms of safety (theft) and other things, what do you advise?
Any tips to prevent theft while tent camping alone in a caravan park?
outdoors.stackexchange.com
<safety><camping><tents><theft>
outdoors.stackexchange.com/questions/13209
outdoors.stackexchange.com/users/9833/RedWolf321
Lock your tent. Leave valuables at home and don’t take anything of great sentimental value. Carry important documents (passport, etc) in a secure wallet. Keep any valuables covered with blankets to make them less attractive to thieves. Carry valuable items (cameras etc) with you  in a backpack. Ask your neighbors to keep an eye on your stuff. Lockers may be available. Be aware of your surroundings. Keep your tent secure, keep critical items with you and leave valuables at home. Make your site and vehicle inconspicuous, use lockers/safes where possible. Exude confidence, follow your instincts.
Lock your tent, leave valuables at home, keep critical items with you. Get to know your neighbours, make your campsite and vehicle inconspicuous. Lockers and safes are available at some sites. Exude confidence, follow your instincts and remember that your life is more valuable than stuff.