Hi pugilist, the only problem shooting on public land is if the wildlife and vegetation is protected. Put a hole in a tree on such property and it could cost you plenty and the loss of your firearm. I would not rely on an email, only an official reply on the correct letterhead may be useful if hassled.
BTW, until you find a place to shoot, you can load up a conversion cylinder with .45 Colt brass loaded with wax bullets and shoot in your basement or garage. The wax bullet is powered only by the primer.