Spare Wheel / Bike Rack Carrier

Hi all,
We're driving from Scotland down to Cape Town, Sth Africa in a Defender 110. We want to take 2 bikes and 2 spare wheels. Heard spare wheels mounted to rear door is not ideal as can rattle door off. Idea is to put one wheel on roof rack and the other on a towbar mount.

Anyone know if you can get a towbar mounted carrier that holds atleast 2 bikes and a spare wheel (or 2)? Would obviously like this to swing out too so can open rear door.

Thanks for your help