Devon was an Associate of the Royal Institution of Chartered Surveyors (A.R.I.C.S.) and successfully helped the family seat at Powderham Castle move into the black. The family finances had fallen on hard times after the deaths of three earls between 1927 and 1935 brought triple death duties. By the 1970s, the family lands had shrunk by 90 percent. The family was in talks to place Powderham in the hands of the National Trust, but the 17th earl backed out when the National Trust insisted on a £60,000 endowment. The castle was opened to the public in 1957.