Yep, I bought a bit of fencing. Ivan bought a row of treated pine logs, all still fun though. I would be very nervous competing in anything more than a skid pan without a harness. I'm ok without a cage as long as I'm not sliding around in the seat.
I have 2 new rotary buckle harnesses in stock that you can use as a 4/5/6 point. $200/set. Obviously you can only fit the cockstrap when you later upgrade to a racing seat with a hole, but the buckle is on the lap belt so they are ideal to also be used 4 point in a recliner seat without the crutch hole. I have the template for the rear mount point too, you can copy it and make your own.