I guess I'm not totally understanding the point of this personal insurance. How much do you really think is at risk? I'd say it's wildly unlikely that someone would steal all of your camping equipment, electronics, etc. - especially if, yes, you're locking it all in the panniers. More likely is that something small is going to get stolen, and at that point, is your deductible and time worth the hassle of making a claim?
In the U.S. at least, most homeowner's and renter's insurance policies protect personal property while traveling.
If World Wide Travel says they cover items that are "with" you, then I think it's fair to say that your camp stove left beside your tent at night is "with" you. I promise they won't send out a forensics team to try to prove it wasn't in your tent. But then... why not lock it up at night?