It's really an impossible question to answer. Nobody here knows what your bills are and what you need to make in order to not only compete, but to survive. Im not knocking and you and I appreciate the fact that you have your hat in hand and are just asking for advice, but the best advice I can give you is the term "labor" is really more effectively translated as time. You aren't charging for labor, anyone can hire a laborer for 15 bucks an hour. You are charging for knowledge and overhead. There isn't a professional company out there that can say "there is really no overhead on this job because there isn't machinery". That would include yourself. Overhead is the 100's of things you pay for a month in order to be a business (business insurance, vehicle insurance, health insurance, office cost, workmans comp, business licenses, truck gas, truck tires, truck maintenance, tools, tool maintenance, cell phone, work dedicated phone, internet... Seriously, this list could go on for a while)...
The point is, you get a general idea of your business operating budget each month (ballpark) and then you break that down into workable days in a calendar month, then break that down into hours and you have what it effectively costs you to stay in operation. The bottom line is, even with all those numbers crunched there are no guarantees how many billable hours you will accumulate in a week. It's far less complicated than it sounds to do all this math, it would probably take about an hour to get a good ballpark figure. The problem is it's intimidating because the reality of the situation shows itself. $50 an hour sounds good from a distance, but it's peanuts. Im a small operation and even when I was a one man operation I would have been broke on $50.00 an hour. It simply doesn't offset the bills in most cases and it requires that you are billing 8 good hours a day, 5 days a week, every week of the year. In most cases, simply not going to happen.