Chief executive officer Brian Scarsbrick said Western Plains Security Network was engaged after the house museum manager Suzanne Grattan "elected not to work out her notice period" following a redundancy.

"Mrs Grattan and her husband, Tim, will remain in the Dundullimal caretaker's cottage until the lease arrangement expires or they secure new accommodation," Mr Scarsbrick told the Daily Liberal on Wednesday.

"An interim management system involving volunteers and experienced paid casuals is being put in place until June 30 to ensure that all bookings are honoured.

"The National Trust asks any person with a confirmed booking at Dundullimal to make contact if they have not been already contacted about their event.

"After June 30 Dundullimal will be closed for three months over winter while repairs and maintenance work are carried out and a new business plan is developed."

Mr Scarsbrick said the decision to make the manager's position redundant resulted from "significant operating deficits relating to the property".

He said the deficit had doubled in the last two years and the house museum had been losing an average of $7500 every month.

Mr Scarsbrick said Dundullimal "needed to get on a financial footing".

"The biggest cost is the salary for the manager," he said.

"We've had to take decisive action by making that position redundant."

Mr Scarsbrick described the July 1 to October 1 closure as a one-off measure.

"We need to develop a new way of operating Dundullimal because the current business model is not working," he said.

"During the temporary winter closure we will be consulting with a range of people to develop a new business plan for the property.

"Workshops will be held with community stakeholders such as the Dundullimal support group, council, managers from other National Trust properties and other tourism organisations.

"By October 1 the property will be open for business with a new system of management to better serve the Dubbo community."

Mr Scarsbrick said Dundullimal was an important heritage property in the National Trust's portfolio of 32 properties across NSW.

"We recognise its importance to the Dubbo community," he said.