The National Archives at Kew (which contain the records of the Colonial Office - mainly the correspondence to and from the Gambia Government). CO 87/142 (1892 files) include a letter from J H Ozanne dated 14 November 1892 from Bosqville, Bog Lane, Guernsey, which notes his appointment as a Travelling Commissioner at £300 per annum and states that he was willing to depart from England to the Gambia on 7 January 1893. In the next file (CO 87/143), there is a letter from Ozanne to Administrator LLewelyn to say that he had arrived at Ballanghar (a port midway up the River Gambia) on 30 January 1893 - so this really marks the beginning of his active service as a Travelling Commissioner.
In Co 87/167 (1902 files) a poignant letter from Mrs M.L. Ozanne (the former Mary Lennox Searle) to the Under Secretary of State for the Colonies dates 10 October 1902. Mary Ozanne noted the death of her husband on 28 February and added that her husband was appointed in 1893 and initially paid £300; this was increased to £500 p.a. in January 1900. She also notes that he was awarded the C.M.G. in 1897 and that he had invested in property in Guernsey. There is a note on the file from H.J.R., who was a senior Colonial Office official, H.J. Read, dated 16 October 2002 in which Read states that Ozanne was a most deserving office and that his widow should receive a compassionate gratuity not exceeding six months of her husband's salary, so presumably £250.