Try them next time you go out! If it is the only cover available in that area they will get on it pretty quick. I have sank Bamboo and caught 6 slabs over a pound each within less than 24 hours of putting it out! One Bamboo bucket produced a 1lb 14 oz slab as the first fish caught there within 24 hours!
I have sank pallets before myself. How many uprights did you have and how much weight did it take to sink it?