Trotman is likely to be given an extended run in the first-team after Preston secured their place in the Championship.
And Irvine admitted he can now start planning for next season.
"There were certainly times when it was looking very difficult," he said. "But since the turn of the year we've played really well and the lads have done a fantastic job.
"They've understood what's been required of them and barring the odd setback they've been fantastic since then."