Former Wales captain Gwyn Jones says Wales should not make wholesale changes for Monday's match against Namibia.
Wales name their team on Saturday morning and are expected to make a number of changes from the side that beat Samoa 17-10 last Sunday.
But Jones is adamant Wales must pick Leigh Halfpenny at full-back to give him vital practice ahead of more testing World Cup encounters.
"I'd definitely want to keep Halfpenny playing at full-back," Jones said.
"The chances are we're going to play Ireland in the quarters if we get that far and the ball is going to be up in the heavens all day.
"It might well be windy and wet in Wellington, so let's play him [Halfpenny] there."
In the opening defeat to South Africa and narrow win over Samoa, Wales coach Warren Gatland opted to play James Hook at full-back and Rhys Priestland at fly-half.
When Hook was forced off against Samoa, with the shoulder injury that rules him out of the Namibia game, Halfpenny impressed in that position after replacing him, setting up Wales' winning try.
The other genuine full-back option in the squad is Lee Byrne, but the 2009 British and Irish Lion has struggled with injury and form this year.
"Lee Byrne, I wouldn't even trust him with a kettle at the moment - let alone a high ball in Wellington - so let's pick the team we're going to play," Jones said.
"Halfpenny needs to play full-back and a few other changes is fine... I think the combinations are important, the line-out struggled [against Samoa]."
South Africa brushed aside Namibia 87-0 on Thursday to strengthen their grip on the top of Pool D.
Wales will also expect to claim a bonus-point win over the weakest team in the group when they meet in New Plymouth on Monday, and Jones says that is vital to keep the momentum going.
"A convincing win with lots of tries for the confidence, a bonus point will help, but we need to get back on track and we need that confidence to play Fiji in the last game of the group," Jones added.
"Then hopefully the Boks do us a favour by beating Samoa and we finish a comfortable second, that's how it should end up with South Africa top."
Hook and flanker Dan Lydiate, who damaged ankle ligaments against Samoa, will not figure against Namibia.
But the game could see the first appearance in this World Cup by Ryan Jones, as the Ospreys back-five forward has been declared fit after a calf problem.
Likewise, fly-half Stephen Jones has been given the all-clear after his injury problems and the Scarlets playmaker is set to become Wales' most capped player by playing his 101st Test for his country.
More from Gwyn Jones on Friday's Sport Wales - BBC Two Wales at 2100 BST