there was a Harpour, Major William Conway residing at Sea View in castletown in 1846 directory, in 1837 Harpur Major William Conway Seamount House - sounds same but not obvious in 1841 census index - however his son entered King William's College in Aug 1833 (in fact he is the 1st in the register !)
Harpur, George Cosby, born May 17th, 1820. Left Nov. 15th, 1834.

Son of Major W. C. Harpur, Seamount, Castletown, I.O.M. Day boy. Medical Student. Died May, 1854, at Seamount, Castletown, I.O.M.

There is a mention - There is a carving in Croft End dating from 1842 for W. C. Harpur Dec. 1842-a major on the strength of Castle Rushen. The land on which Crofton, Westwood and Elderbank now stand was occupied by the Lord's Garden belonging to the Governor in 1833. In 1835/6 it was sold to Thomas Brine, the architect, .. in www.manxnotebook.com/iomnhas/v074p686.htm

BTW is the Margaret Harpur of www.manxnotebook.com/fulltext/an1847/p465.htm related ? - there is a douglas Harper ? family with a will of Wm Harper that seems to fit the family.