Humble can also play either position but could be challenged for fullback by Reddy, Beau Ryan and Mitch Brown, while youngster Jacob Miller will compete for the halfback position.
"I feel comfortable in the halves," Humble said. "I like tackling more than catching bombs."
Reddy has played most of his career in the centres but faces a huge task ousting Test star Chris Lawrence or Blake Ayshford, who enjoyed a breakthrough season this year.
Bought largely for his tough defence, Reddy said he was prepared to play anywhere in the match-day 17.
"A few things obviously changed after I was signed," Reddy said.
"A few positions were still up in the air and obviously the Tigers hadn't made all their decisions before I came here.
"Fullback, back row, centre, winger, it really doesn't bother me.
"It's not as if I can just walk into the team. It's going to be a tough grind just getting in there."
Moltzen led one of four teams in a merciless pre-season strength session on Friday.
Dubbed the strongman challenge by the club, pairs of players flipped a 300kg tractor tyre up and back over an 80m course.
Individuals hauled a beer keg full of water weighing 75kg before painfully pumping huge ropes borrowed from an ocean liner.
Ryan said Moltzen, who the Dragons accused of misleading them, had done it tough during the contract wrangle.
"I'm not sure who was at fault there but his name got dragged through the mud a bit there, which is not good, to see a friend go through something like that," Ryan said.
"(With the Tigers) going so well over the last few years, he wanted to stay a part of that.
"He lives in the area, his family's from round here and everyone just wanted him to stay."
Also close to several Dragons players, Ryan said the 2010 premiers were fuming over the backflip.
"Definitely they're upset," he said.
"I'm close with Matty Cooper, Dan Hunt and a few of them and they really wanted him there."
- AAP
