Seems there are many ways of approaching this, David`s is particularly neat. Andy`s clearly shows the underneath supporting plate. A winch exerts a lot of power, so it needs firm locating. Rvanvoris, make sure you incorporate good support under the box for your winch.
Andy, the chain goes below into the anchor locker (where I had head and arms changing the footswitch). I store the snubber, a strop for extending public mooring lines, pipe arm for winch gypsy, and an unused Anchor Buddy I got with the boat .
The IG Europa I saw in Qld. had a teak grate from bulwark to bulwark, but was open underneath.
Note my aft port winch fixation cannot bolt through, it needs a coach-screw into wood, but the screwhole is "screwed". To avoid R&R of the winch, I`m trying devise cleaning the hole out and epoxying a plug into it, winch still fitted. I think it can be done.
Island Gypsy 36 Europa "Doriana"