Check out the rail setup I use in this thread:
https://www.tinboats.net/forum/viewtopic.php?f=48&t=22675&p=231785
Its design allows for use on multiple boats. As for a platform, it all depends on how extravagant you want to go. In my old 14 foot duracraft, I used a sheet of plywood laid across the width of the boat.
For my 16 foot Triton, I modified the existing deck to a single level, it's about 5 foot wide, and 5 foot long, lots of room to stand.
Check out the pics in this thread for some ideas on framework and a platform:
https://www.tinboats.net/forum/viewtopic.php?f=21&t=24987
And here's a flounder gigging video, aboard my jetboat:
https://www.youtube.com/watch?v=uq7cLEJLKoo