Those encouraged to register for the trial are standout union and league players born from 1996-98.
Mann said they would be arranged into nine-man teams based on their current playing grades and any scouting knowledge the Warriors or Mid Central staff already had on them.
However, at every trial a player who had been completely off the radar would show up and draw the interest of the franchise, he said.
"It happens - last year a guy came down from Kaikohe, hadn't been with the league scene up there.
"This boy came from Nelson College, 1st XV, had played a little league - from out of the blue.
"There are boys from Australia, coming back from having gone over at a young age and it didn't quite work out, and they come to have a crack."
The wider lower North Island region has proven rich for NRL-level talent.
NRL premiership winner with Souths and Warriors-bound hooker Issac Luke hails from Hawera, while former Warrior and current Penrith Panther Elijah Taylor attended Patea Area School as a youngster.
Their fellow Kiwi international Tohu Harris is from Hawke's Bay, while Russell Packer is from Foxton and the Brisbane Broncos brothers Kodi and Jayden Nikorima were born in Palmerston North.
Three of this year's Junior Warriors regulars - wings Tomas Aoake and Paul Ulberg, along with loose forward Jazz Tevaga - ultimately gained contracts through their performances at the club's NYC trial.
Mann said the Warriors staff would work closely with Mid Central general manager Lisa Reweti and her team.
"It's hugely exciting for us to be able to take a trial to Wanganui and we're really grateful for the enthusiasm shown by the Mid Central Zone.
"Our aim is to give as many athletes as possible the opportunity to trial.
"While we have a scouting network which identifies most of our talent, our open trial concept has also been hugely beneficial in giving us a look at other contenders.
"By having two trials we'll be able to offer an opportunity to a wider group of players."
Visit http://www.warriors.kiwi/news.html to get the link and fill out the online application to appear at the trial, or email academy@warriors.kiwi for more information. The deadline to apply is October 1 and those chosen to trial will be notified the following day.