There may be a simpler way... on the router, make sure UPnP is enabled. There used to be a Tablo setting that had to be checked for remote streaming, but it looks to be gone. But, UPnP should set the protocol and ports automatically.
When I look at the mapping table on my router under UPnP, there are two entries, both with TCP protocol. For the first entry, Internal port is 80 and external port is 21030. For the second entry, internal port is 8887 and external port is 21031. Note that I'm also using address reservation to give Tablo a "fixed" IP address, which is also in both table entries.