The visitors saw Mark Little sent off in the first half but Rovers had to settle for a point, with Jeff Hughes grabbing a 57th-minute equaliser.
"The lads are down in the dressing room because we didn't win against 10 men. But we showed character to come back from 2-1 down and create two or three more good chances," said Campbell, who is in temporary charge.
"During my time at the club we have never played well against 10 men and you could see why Peterborough are where they are in the table.
"[Craig] Mackail-Smith does the work of two men up front and they have some other talented players. I thought we dealt with them well and I still believe we have what it takes to survive in this division.
"Our next game is away to Yeovil, which will be a huge one for both clubs, but we can go there with plenty of confidence."
Source: PA
Source: PA