If I may expand your concern a bit, think about what you do to protect you and your stuff on tour. First, we try to maintain situational awareness, whether we are on the road, or in a campground. Second, unless we have our bikes in plain site and complete control, we always lock the bikes to something (yes we lug around Kryptonite Locks and Cables). Third, we keep our stuff out of sight much as possible (in panniers when stopped and zipped up in the tent in the camp ground). Finally if it's valuable, we carry it with us (we use the little straps that come with the handlebar bags). And, as best we can, we keep our eye on our stuff.
Is this a sure fire recipe for success? I wish it were, but the best defense seems to be to attract as little attention as possible, and make it at least a little less easy than it might have otherwise been.
I think it is easier with two people, but it sometimes means you don't just leave your stuff on the spur of the moment and walk down to the beach. You have to plan it out a little bit.
Having said all that, remember the first rule of touring -- have fun!!!!!! Try not to get yourself into vulnerable positions, and take reasonable steps. Don't let this fear spoil a wonderful opportunity.