I see this has been up for 20 hours with no replies... Perhaps if you change the title to: "Haunted Corn Field, NEED ADVICE", you might attract the responses you're seeking? I know for a fact there are some very knowledgeable haunted corn field owners who haunt these forums. From what I've been told, fire regulations are MUCH less restrictive for an outdoor haunt, but I believe that varies from place-to-place. You might try contacting Eric Lowther of Haunted Overload ("elowther" on these forums). He runs an amazing outdoor haunt in New Hampshire (where you said you want to hold your event). Good luck to you!