Ditto to all the above, particularly for the need for investigating the local bylaws and how they apply to this business idea.
As for a "truck" ... if I were to be a customer, I might be more intrigued if it were a well-stocked RV, where I could go inside to shop. The consumer would have more of an assurance that the goods had been handled with care (ie farmer's markets are often outside and in the rain!) And from your vantage, there'd be minimal set-up/take-down between stops.
Can you carry enough inventory to be of "value" to the consumers? I understand your interest to fill the distance to an LQS problem, though if you can't compete with your inventory and pricing, the customer might be more likely to go the extra distance. I know that I often drive by one LQS, knowing that the other one, just a little further has a larger variety awaiting me.
Do your business plan and see what your start up would be, and then if the potential $ale$ are going to reap a profit? or be a deficit? Good LucK!!