A lot depends on where you are. Indy mentions situational awareness and that is always important. I tend to take what I consider reasonable precautions for where I am. That may range from not worrying about locking at all in some places to never leaving my bike out of my sight in others.
These days I carry a very minimal load, but when I carried a more typical load with panniers, the panniers stayed on the bike at alll times and nothing went in the tent execpt what I needed to sleep and the minimal amount of valuable that stayed with me at all times. To be honest it is very rare that I worry much about any gear theft issues in camp when staying in a campground. My gear tends to stay packed and out of sight when not in use so there isn't gear spread around for someone to browse through. I tend to shower very quickly so stuff isn't unattended flr long. I tend to make friends with neighbors so someone poking through my stuff is likely to be noticed.
I think if I were really that worried I might ask someone who was in their camp if I could park my bike with it's loaded panniers in their site while I was in the shower. I doubt I will ever do that. but if you are really worried that might be an option.
Signing in to your site and leaving something to reserve it so you could shower before setting up camp might be an option. You could leave everything in what you deemed a safe location or wheel it in with you. Again not something I'd be likely to do, but...
My ultralight packing style would allow just carrying everything with me to the shower with ease, but I have never bothered to. In cases where there has been a shower I have generally considered it safe enough especially after making friends with neighboring campers.
Of course there is always some risk. I just accept that at some point in my touring career it is possible that all my stuff could go missing. It is easier to accept that if you have gear that you can afford to replace fairly painlessly. I figure that I''d be able to continue a multi-month or even a multi-week tour with a short delay and ending a short tour early wouldn't be the end of the world given the unlikeliness of it happening with any frequency. If that were to happen I'd try to look at it as a chance to retool. Most of us will tour our whole lives without that happening with even very minimal care and a little situational awareness.