I've had a couple fitted to previous Defenders and I found the ones opening with the rear door really convenient. The brand I fitted had a rudementory "piston" type arrangement that soaked up vibration. The piston would retract on opening the door and extend when it was closed. They were sold as "Africa Specification Wheel Carriers" and those who get the UK Landie mags will see them under Craddock's and Paddock's ads. OL seems to have one that might be the same arrangement?
I'm over a 100kg and I regularly stood on the spare to pack things on the rack and I never had any problems with bending, cracking or sagging.

