Carro will vie with Will Freeman for keeper duties.
Goal-getter Charlie Cook has also arrived from Coventry United but it will be one in, one out with full-back Marc Passey having moved to the Midland One pacesetters.
Another to leave is full back Marc Passey, who has moved to Coventry United, with striker Charlie Cook expected to come in the opposite direction to Banbury Road.
“It’s disappointing to lose Crossy, but I understand his reasons and we wish him well,” said Constable.
“We quickly moved in for Nathan Carro, who is one of the best keepers on the local scene, and is desperate to step up and test himself.
”Charlie will be a big hit with us and will score plenty, I’m sure. With Ben Purser and Tom O’Callaghan also up front, we’ll definitely be a threat to any opposition”
Another young player signing on is Johnny Adair, who Constable describes as “coming with a good reputation, having played for the club’s junior teams in the past.”
Southam are in action on Wednesday (14th October) when they travel to free-scoring Nuneaton Griff.
Carro and Cook, who were ineligible in Saturday’s 4-0 defeat to Triumph Athletic, are expected to feature.