Mo1, welcom to 360tuna.
Harness is not a must for tuna fishing, but it will help a lot.
Another methode will be using the rail, most efficient way in my opinion, but less sporty than of harness. JMO
for reel that doesn't have harness lugs, i use "Get Strapped Bracket"
or rod rings for spinner.
Sorry Jedi243, you post while i was typing.
Good advice, thanks