Backs coach Gibbs said there was still a concern about lack of depth in key backline positions.
"We have seen growth in some of the boys. I think Dan [Hollinshead] has had a very productive year with the time he spent with the Chiefs. The New Zealand [under-20] process was good for him but unfortunate. I think he has grown a huge amount out of that. His attitude has been second to none.
"Te Rangi [Fraser] has probably been the standout back of club rugby to date. I am happy to see those boys growing with the game. It is not an easy fix and sometimes it is time in the saddle. It is really important we don't throw them out just because they are young.
"Midfield is an area we have looked really hard at. We are looking for guys that do specific things ... that are going to transfer into ITM Cup."
McMillan and Gibbs are working with a wider training squad ahead of the official Steamers trial on Wednesday June 17 in Rotorua.
The squad will train together over the next six weeks as ITM Cup preparations ramp up with the start of the competition now under three months away.
McMillan is not making the squad public at this stage as he says it is a fairly transient group, depending on form and injuries.
About 75 per cent of their final squad was sorted.
"I am happy the squad reflects club form and the profile we are looking for in an ITM Cup player. However there are still seven weeks before we make our final selection. There is ample opportunity for the players who have missed out on the initial squad to put their hand up.
"Consistency of performance as the competition nears the play-offs will be vital to enhance their chance of selection."