8 Lodge
9 Macca
10 Ofa/TPJ
11 Sua
12 Gillett
13 TPJ/Ofa
14 Staggs/Kahu
15 Glenn
16 Haas
17 Mago/Fensom/Carrigan/Taga
Looking at the way Seibs approached his bench rotation with souths last year I would not be surprised to see Glenn as a regular on the bench. I think he would play the Cam Murray role where he comes off the bench as part of the middle rotation. I don't think the other second rowers are really suited for that workhorse type role in the middle.
From memory Seibs started Surgess at lock but moved him to prop when Murray came on. In terms of the Broncos a guy like Offa could fulfill that role. I believe Bennett did a similar rotation with Moose being the middle that would be last subbed off.
I think Sua and Gillett start the year and play out the 80. Alternatively Glenn could start at left second row, move to lock when TPJ comes off with Sua or Fifita to come into second row for remainder of the game. Glenn then gets taken out when the props return and stays on the bench.
I also wouldn't be surprised if Kahu ends up being Seibs preferred utility given he covers wing, centre, fullback and 5/8. Staggs can cover center and second row but I'd be very hesitant to throw him on the wing, which is where you'd think he'd end up with Bird and Jimmy in the centres. We'd also have very little cover if a half went down if Staggs was on the bench. Seibs also had Doueihi off the bench last year giving him backline cover, showing his previous preference