Wanganui missed an early chance when Robinson charged down a kick and fed Kubunavanua, who had an open line but passed to the better-placed Waara, who could not hang onto the wet ball.
However, Waara swiftly made amends as the glue stuck when he swept up to make an intecept and run under the posts, which Robinson converted to follow his earlier penalty kick for 10-0 after 17 minutes.
Loose forward Kieran Hussey then went blindside and put through a good chip kick with Waara right behind it to trap Wellington Maori in their own corner pocket, with the home pack then driving prop Marek Willis over for 15-0.
Wanganui would score two more tries through Waara and lock Josh Lane to put themselves comfortably ahead in the closing stages.
"[Wellington] got a try right at the end, We had one red-carded, so a bit short," said coach Denis Edwards.
Edwards said Willis got frustrated with a player lying on the ball and rucked him - the big no-no of the modern game.
No doubt it had helped to have quality players like Robinson and Waara available.
"I was always hoping to bring them up, but that depends on who drops down from Heartland," Edwards said.
"That's why we end up short on the bench."
The team had struggled initially when trying to play dry weather rugby on a ground with lakes in the in-goal areas, although Wellington Development were guilty of the same thing, especially in their own half.
"We got the better of it with two intercepts," said Edwards.
"Our forwards played quite well, especially in the second half.
"They need to learn to play territory rugby, and then they'll be a very good side."
