I’ve been having a battle with the stupid seatbelt warning. The manual has a workaround for shutting off the seatbelt warning but I haven’t had much luck with it. Something about turning on aux power, buckling and unbuckling the seatbelt 4 times, then supposedly it turns off the warning for that seat.
Just buy some of those seat belt buckles on Amazon and pop one in when you don't want to buckle up. I am pretty sure you can get 2 of them for less than $10. I use one all the time when I am off-roading slow or at the deer lease and getting in and out a lot. It just thinks it is always buckled.