Here's some options ...
1) There is a hardwood pad affixed into the Parker bilge you can screw into, one forward and one aft im my '92 vintage SC. when it is 'too far away' from where I need it ... I use aluminum or Starboard-type (but cheap HDPE) strips to bridge from the pad to the float switch or even pump.
2) A slick method I like is to take 1" or 2" flat-head screws and epoxy them upside-down into the bilge, using the switch box or pump strainer base as the 'bolt pattern'. Once the epoxy cures, attach the item to the bolts which now look like head bolts affixed in your bilge.
Make sure to 'hold' the bolt right above the epoxy with vice-grips when you put down the nuts, one below the item (so you can level it to the water, not the bilge "V") and one on top to hold in place. See sketch!
3) Sure, a hardwood pad would suffice. It would take 20-years for a piece of mahogany to rot out when exposed to saltwater anyway.
4) Though a last choice option, you could wire tie it (use backups too) to a fixed item, like your seacock.
Lastly, a thorough CHECK of all such bilge items should be checked before running the boat, while in use, and before heading back in ... at least IMHO.
I also run a high-water alarm in the bilge (mounted higher than the pump float switches) and it works so good that some water droplets got splashed on it when I hosed down a 'gold' reel the day while offshore. Man, just one little drop got to it and BEEEEEEEEEEPPPPPPPPPPPPPPPPPPP :shock: !!!