On a trip of 6000 miles I had boards lashed to the stanchions and plastic 25 litre plastic "cans" of fuel and water lashed to the boards. We sailed in a lot of bad seas and the problems we had were:
- Cans moving almost imperceptily at first, fidgetted away on the deck and did susbstantial damage on the non-skid.
- Eventually they loosened the stanchions in their mountings and started moving more and more.
- At one place the cans were on the ends of the jib car tracks and the tracks started to work loose with associated problems of stripped screws and water leaks.
The things that survived best were the plastic cans!! They showed no sign of wear.
Once we became aware of these problems we ensured that we decanted the liquids into their respective tanks at the earliest opportunity to make the cans as light as they could be.
If I did this again I would make up some sort of shallow timber tray with decent securing methods to bolt the tray to the toe rail to contain the cans and stop the fidgetting and movement. A 25 litre can is quite heavy and the inertia of the can when the boat is jumping around is considerable.
But I have to add that I will go to great lengths to have storage of additional liquids anywhere but on deck.