5050 is the correct primer for polysulphides, the polysulphides are normally 2 part and don't require a primer unless fully submerged.
i would use 206 and a single
for on deck
or portholes, much easier to work with and they do a great job, sulphides require Exact mixing procedures and precise quantity for each part if your taking a little out of each kit. they will also need to be used quickly as pot life is not extensive ,if using sulphide the pot lives can be extended by asking for different pot times they sell slow medium quick in most of the sulphides. (206 reacts with sulphides)
Hope this helps