As far as an overlay map, your best option would be in Donald Frazier's book COTTONCLADS! The Battle of Galveston and the Defense of the Texas Coast. This book has the fighting areas of the Strand well marked on pages 71 & 72. The book is on a high school level, but still is good.

A much more detailed account with maps by Donald Frazier is Battle on the Bay: The Civil War Struggle For Galveston by Edward T. Gotham, Jr. UT Press: Austin 1998.

A wartime map of Galveston and its defenses, and the one I use in my classroom, is National Archives Record Group #77, Civil Works Map File Q-102. This map was made by the Union Dept of the Gulf under Maj. Gen. Nathan P. Banks. It is a real treat and one can easily match locations from those days with current locations. Needless to say, it is not an overlay map.

I hope this answers your question and I wish you the best of luck!