David,

You're in a no-win situation.  So is your employer .. and that is what he is, an employer, not a customer.  If you were a true independent contractor he would be a customer.  If you bring this up he will probably find he doesn't need your help any more.  But if he continues the way he has, unless he is paying you exceptionally well, you are getting the short end of the stick.  And if something happens to you your widow might own his farm. 

If the IRS comes in he is not going to be happy.  If IDOL (Illinois Department of Labor) shows up he is going to wish it was the IRS.

He is in a no-win situation and so are you.  He needs to do what is right for his benefit as much as, or even more than yours.   But I suspect if you bring it up, next season he won't call.