He wants to build a portable, floating dock to launch kayaks and canoes along a ever changing banks and locations. He already have the blocks and he was wanting to keep the dock as light as possible so it can be broke down and hand carried from location to location. Has to be big enough for up to 3 people to stand on at the same time but stable enough not to roll if two of them are to close to the edge like when getting into or out of a boat.
The blocks are strong enough to stand on without denting or falling apart so the glass/epoxy would be to keep the foam from being damaged from transporting and heavy things from breaking the foam apart.
If they were made into 4' X 4' blocks that use 2" PVC pipe that locks them together that also serve as grab rails, would that be stable enough between the joints? The pipe would slide down into sleeves epoxied into the foam. He understands that the glass will delaminate from the foam but if the top and sides were thicker and a thinner bottom would that help hold it all together?
Like I said, asking for a friend.

"that it isn't just an ordinary sort of boat. Sometimes it's a Boat, and sometimes it's more of an Accident. It all depends." "Depends on what?" "On whether I'm on the top of it or underneath it."
A. A. Milne