1st, it's too bad you even need to worry about it but I suppose most of us do to some degree.
No, I've not installed any locks. The cabin door has a "lock" - such as it is, but's it really only "suggests" security instead of actually being secure.
I don't leave anything of significant value on board when I leave the boat. Cheap PFD's, some lines, boat hook and cleaning brush, engine flush muffs, the anchor. The stereo face and GPS are removeable so I never leave them. Aside from those the only things of significant value are the batteries.
One school of thought is that if you make it more difficult (locks) the low lifes will move to an easier target. My take: The boats are plastic. Meaning, if someone wants "in" bad enough they'll just pry it open with whatever implement they have on hand. I'd rather them take what they want instead of damaging the boat.