It's common to have rollers on a bunk trailer to prevent the keel from contacting the frame when loading or unloading the boat, sometimes rubber pads are used, but rollers are better.
Cracks in the strakes can be serious, or not an issue, it just depends on the method of construction. Some strakes have a relatively thin layer of glass put down, then are filled with something to make the inside surface flat for easier lamination. They may be filled with putty, foam, wood, floor sweepings, it doesn't make much of a difference, you just need to fill the space so it can be glassed over. If the glass isn't thick enough, or the area takes a good hit, then it may crack, but it doesn't leak into the bilge area, it will only leak into the strake itself, it's not good, but it's not a safety concern. To know which it may be you need to inspect it, you can't tell from the outside unless you open up the crack and see what the build method is, the better method is to look from the inside.
