The Lions started the day on 43-3, already with their lead of 307 likely to be far too steep for their opponents.
But rather than declare, Trott got another opportunity to score some runs on his first match back on international duty, alongside wicket-keeper batsman, Sam Billings (53), who was one of four from the squad of 15 to miss out in the first innings.
The pair put on a 115-run partnership together until Billings was retired shortly after reaching fifty.
Jonny Bairstow perished for a duck shortly afterwards as the Lions looked for some quick runs before the declaration eventually came on 176-5.
That gave them a lead of 440 and a scheduled 56 overs to try and dismiss Gauteng for an opening tour win ??? plenty, considering they skittled them out in 50 first innings overs.
But that wasn???t the case ??? an??approaching electrical storm meant the innings and the match was concluded early with??only 42 overs bowled and??Gauteng finishing on 120-8.
The workload was shared between eight bowlers as – like Billings with the bat – Adam Riley (1-8), Matt Dunn (1-11) and Craig Overton (0-9) got a first run-out with ball in hand.
Overton was the only member of the attack to go wicketless, albeit from only four overs bowled, with Adil Rashid picking up the best figures of 2-14.
It was a strong opening to the Lions tour, with Trott???s runs added to first-innings centuries for Adam Lyth and Sam Robson as major positives, and a win in all but name.
A much sterner test awaits the squad next as they move on to Boland Park in Paarl for the first of two four-day games against South Africa A, starting Sunday.
The two will then play five one-day games before the tour ends in early February.