I would like to update this thread.
https://www.backroad4wd.com/
Washington State based 4 wheel drive trainers.
We are currently booking our September 101, 201 driver course.
Does the spare fit in the stock location? If so use it. Just be cognizant that you have low hanging fruit and if you drop a rocky ledge you could damage your spare.
In my GX 460 my drawer box is 64" long with additional leg on the front that kicks up its, 75.5" long and 32" wide at the shoulders. Of course with this drawer/platform the second and third rows are removed. But it gives you and idea on space available...
If you haven't heard of Kaon, they build a few items for the 120s. I was surprised they have less for the 120 vs the 150.
https://www.kaon.com.au/rear-door-table-and-cage-to-suit-prado-120
I ordered and installed the rear door table on my GX460. Shipping and cost was not bad due to exchange...