I may be wrong, but is it a fact the double decker design prohibits and afterlife as a freighter?
Is that because the head room of each deck is lower than a single deck and is the floor of the upper deck strong enough for freight.
I don't know the answers but wouldn't it to some extent depend on
A) the size of individual items
B) total floor weight limit
C) even weight per sq foot for smaller but heavy pallets.
D) can you fit one huge double deck freight door or would you have two one at the front for lower deck and rear for upper deck