Great letters! I particularly liked the mention of his early voyage with his sister (not sure which one - probably Violet) and father, Captain Joseph Boxhall, with the Wilson Line's Alecto. Captain Boxhall also took his children further afield as well - one travelled with him on one of his ships as far as India.
I thought the line in the last letter about the revived interest since ANTR getting 'rather more' than he could cope with terribly poignant. Initially he seems to have welcomed it, but eventually it seems to have become rather too intrusive. Also the repetition of the Alecto anecdote in several of the letters, as he's not sure if he related it before. It was a few years after this that he began showing signs of memory loss, and I wonder if this is a very early manifestation?
Sadly you are apparently correct, Shelley - not many of his personal papers seem to have survived. He and his wife lived in rather reduced circumstances in a council house, and he was eventually hospitalised. After his wife's death few years later, the flat was ruthless cleared. Some personal items (e.g. his medals) were sent to his wife's family, who very generously did the decent thing and returned the items that had been Boxhall's to his side of the family. But of his correspondence and most of his photographs, few have surfaced (one can hope, though!). Fortunately his family have many photographs of their beloved 'Uncle Joe'.