The Immune Deficiencies Foundation of New Zealand installed the partially mobile home - its first in the South Island - at the camping ground in late October.
Michelle and Shane Thornton's 2-year-old son Tristan was born with the rare genetic primary immune deficiency disorder Di George syndrome and no thymus gland.
The gland, just behind the breastbone, produces cells which help the body fight infections.
In October 2007 Tristan underwent thymus tissue transplant surgery in the United States, after being kept in isolation since birth.
Mrs Thornton said the past three years had been difficult, with Tristan unable to be taken away from home until recently.
A week at Bannockburn almost completely cost-free had been a welcome opportunity for family members to spend time together, she said.
Seven family members stayed at the $130,000 self-contained home.
Mr and Mrs Thornton were handed keys to the home by Central Otago Mayor Malcolm Macpherson on Monday, to mark the first use of the facility.
The foundation's other respite care homes are at Otaki, on the Kapiti Coast, and in Auckland.
They offer foundation members and their families a place to stay away from home at minimal effort and cost.
