The weight problem is solved with stronger bits in the ends of the boxes.
I used box sets. Another poster mentioned using cut plywood.
The fact is a well filled box is going to be MUCH stiffer and stronger than one not fully packed.
It is the flimsy partially filled boxes that will fail!
I stacked my packed boxes FIVE boxes high. No problems.
A fully packed and stiff box has far more strength than a partially or 'loose' box!
Packed the LPs act as part of the box, and the cardboard is really just holding the LPs in., loose all you have is the thin cardboard for vertical strength