When I ship a plant in semi-hydroculture, I cover the top of the medium with paper, then tape it down to the pot with masking tape. I drain the liquid and put tape over the holes to reduce the chance for leakage.
The plant is then surrounded by shredded paper (a pad, insulation, and absorbent), wrpa that in closed-cell foam, then wrap that in more paper.
It certainly adds weight, but not a lot compared to soppy sphagnum.