Via BikeTrailerShop.com Email:
Having had things stolen from the baskets on my bike when I was in a store shopping may I suggest that you develop an around-town cargo trailer that can be locked.
I thought I would answer this question under the two-wheel trailer forum, although the discussion will apply to some uses of single-wheel trailers as well.
When it comes to locking bike trailers, there are two important aspects, locking the trailer to the bike and/or a bike rack and locking up the contents of the bike trailer.
For locking up the bike trailer itself, we generally recommend getting a cable lock that is long enough to wrap through one or both of the wheels, the bike trailer frame and up to the bike. If a ulock is being used, this can lock to the cable the bike frame and a bike rack.
There aren't that many bike trailers that come with locking mechanism's for the cargo. One of the few trailer that has this built in is the electric assist bike trailer, the Ridekick, which comes with a hard shell cargo area that has a locking closure.
A good option for around town is mounting a lockable container to a flatbed bike cargo trailer. A direction that we recommend is utilizing a Wandertec BONGO (large or small). A 24 Gallon Rubbermaid ActionPacker can be bolted directly to the frame. The Actionpacker can be have both handles locked shut with pad locks.
Another option is to use the Pac-Safe 120 bag lock. This wire mesh lock will wrap around duffel bags. It works very nicely with the BOB DrySak or the Ortlieb RackPack XL. This is a good option for touring with a bike trailer and wanting to lock up your stuff.
It should be noted that most of these locking mechanisms are fairly lightweight and are intended to stop the casual but not necessarily a serious, determined thief.