I was thinking about the roller blade wheels for a while when I did my beach cart. Right now I have some very slippery industrial "trex" type decking. The stuff was actually 2x8 dimensions. It was from a fishing boat builder. The single 4' board got ripped in half and I used half for each bunk.
When I redo my trailer, I'm thinking about 2x4 treated lumber, but then go to my plastics dealer and have them cut me some strips of 3/4" UHMW 1.5" wide, then counter sink screw that to the top of the lumber. Probably router the edges a bit and call it good. Either that or get more of that "trex" stuff from that boat shop.
The one thing about using anything slippery for bunk material is that you NEED to have the pin in or the strap on when backing down a boat launch or you skis will end up on the launch. Right now I unpin/unstrap my skis up top, the carpet holds them really well.