Bill, as a self employed person, sole proprietor, I never thought this was necessary. And, keep in mind that with most workman's comp cases, you have to incur an injury on the job in order to collect. I would think the premiums would be very expensive.
Wouldn't it be less expensive to purchase disability insurance? A policy that provides you with a paycheck when, God forbid, a long term injury, or worse yet, illness, prevents you from working. Most physicians I know have this type of policy, but I only know of one that managed to collect on it when his carotid arteries plugged up and he no longer perform surgery. Even then, the insurance company did their best not to pay him and he had to sue them in order to force them to make good on the policy.
Now, if you were employing someone else, a female vocalist, roadie, etc..., then, at least in Maryland, by law, you would be required to provide workman's comp insurance. I had to do this when I had a guy working for me when I owned a fishing tackle and boating store, and it was quite expensive, even way back then.
Good luck,
Gary