Misner Haven coastguard station was on the East coast near Southwold. Downderry is on the Channel coast, just east of Looe in Cornwall. I've not heard of Deownes and suspect you have mis-spelt or misread it.
I have a number of Tiltman's in the coastguard:
1. Henry Tiltman joined Cockleshell Hard from Elmer 16-Dec-1819, and removed to Orford Haven 15-Jan-1823
2. Howard Tiltman joined Minster from Newhaven 30-Jan-1819, and removed to Shellness 10-Aug-1819
3. Thomas Tiltman joined Warden Point from Minster 10-Aug-1819 and was still there in 1822
4. Richard Tiltman joined Misner Haven from Mundsley 8-Oct-1835, and removed to Crouch River 23-Aug-1837