If the 25 is like my 22
then it has a solid fiberglass headliner/cabin insert. On my 22 this liner was no longer (if ever) flush with the cabin top. The cabin top is cored fiberglass which will have either a balsa or marine plywood core sandwiched betwixt two layers of fiberglass. If this liner is flush with the cabin top, I wouldn't see any problem in drilling through both and attaching the hardware with large washers or backing plates. If, however, it is not longer flush with the cabin top you will need to drill larger holes in the liner so you can access the underside of the structural cabin top. Then you would mount in the normal way. Backing plates or very large washers will be critical for this as the turning blocks will have quite a large load on them, especially when being winched. Search the archives, there was someone who detailed running lines aft on a 25. They had some nice pictures and I believe they even had pictures inside the cabin (If I remember correctly, they had to cut large holes in the cabin liner). Good luck!
