Presumably, you are using FileMaker 13. Popovers are not possible in older versions of the software.
I don't have any clue at this point as to exactly how your database is designed to store this information, but the following general info may provide you with the needed clues to get it working. If not, you'll need to use Post a New Answer to describe your database design in more detail.
it seems likely that you can place the popover buttons directly on top of the map graphic. The popover button can be sized to cover the portion of the map representing one boat slip and given transparent fill and border colors to make it invisible. (I would not make the popover buttons invisible until I first get them to correctly display the desired data.)
If you open the popover, you can select the popover panel and set the onObjectEnter trigger to perform a script. This script will then be performed each time that you open the popover. You can specify a script parameter to be passed to that script with key information such as the ID of the boating slip that corresponds with that particular popover.