Thanks for all your suggestions guys!
I know the cross member is not in the best shape. I have some what treated the area to get me through a couple more seasons hopefully.
I have sprayed them with wd40 and let it soak In . Tried to undo it with sockets but the nut keeps spinning they are to far gone as Noel suggested.
I have an Idea of drilling a hole ( pilot hole first) through the nut then again at roughy the same size. Then grabbing a cold chisel to spilt the nut in half. After that hopefully jimmying the bolt out with a screw drive. I could also cut the bolt head flush try bashing it out like Noel said but not keen on whacking it to hard in fear cause more damage. It’s not a user friendly design I think ( the bolt and nut combo).
I don’t have blow touch might have to get one , to help.