However, reserve Ranato Tikoilosomone stepped up and was influential in the final 25 minutes - scoring Wanganui's final try in the 73rd minute after some good runs and tackles.
Lock Fraser Hammond was back to his best after illness, as was flanker Daniel Fitzgerald in returning to the starting lineup and playing the full 80 minutes, with his shoulder coming through nicely.
Coach Jason Caskey and captain Peter Rowe praised Perofeta, whose ability to spot the gap and turn on the gas is a real asset at this level.
"He scored a couple of nice tries. You can't fault him too much for a young guy," said Caskey. "The obvious thing to pick up is a bit of communication and direction."
Much like his whole team, Perofeta is a natural attacker but sometimes in games consolidation is the key.
Caskey said Thames Valley's eight points in the first half were gifts - a penalty given away in front in the posts in the opening minutes, and then an attempt to spread by the halves which saw the ball cannon off a supporting Wanganui forward's head, into the hands of Thames prop Haerengarangi Renata, who dashed away.
"It was something you see in the circus, rather than the rugby field," said Caskey.
Wanganui got their third try from winger Samu Kubunavanua after 30 minutes and Perofeta earned the bonus point not long after halftime for 26-8, at which point their play became a little haphazard.
Caskey said there were times when swift exit of the ball from the 22m was needed, but the side threw it around and gave away turnovers. It was only when Thames Valley were within five points of the lead that Wanganui got back to their own systems, as Perofeta got his second try and then reserve hooker Cole Baldwin and Tikoilosomone scored.
For the home team, winger Lance Easton grabbed a double and hooker Hayden Wisnewski got the other try as they salvaged a bonus point.
"It was a bit helter-skelter," said Rowe. "It was a real funny game. We played some good footy and then some ordinary stuff."
After last year when Wanganui could not beg, borrow or steal a victory on the road during the round robin, the team lifted their away game record to a perfect 3-0 in 2015.
"We have been playing well away from home. But it's not easy, even here, especially playing a team with a guy having his 100th game," said Caskey.
Unfortunately, in the race for the Meads Cup home semifinal berths, both Mid and South Canterbury matched Wanganui with bonus-point wins on the road this weekend, maintaining first and second spot respectively.
Therefore, Wanganui must keep their foot on the gas at home against Poverty Bay on Saturday, although Caskey will want the team to just concentrate on getting each victory, rather than trying to out-do what the Canterbury teams are doing elsewhere.
"We're focusing on our job. We've got two games and we'll just get our points."
Rowe was of a similar mindset, even if the current scenario means the team might have to travel to the South Island twice for Meads Cup playoff games. "If you want to win the competition, you have to win against anyone and anywhere."
Wanganui 47 (Stephen Perofeta 2, Bryn Hudson 2, Samu Kubunavanua, Cole Baldwin, Ranato Tikoilosomone tries; Trinity Spooner-Neera 6 con) bt Thames Valley 27 (Lance Easton 2, Haerenarangi Renata, Hayden Wisnewski tries; Jonnie Te Ruki 2 con; David Harrison pen). HT: 21-8.