One option you can do is to choose a cleaner tiled texture off of say CG textures. Then you can extract a mesh ring around the top and bottom of the tanks to apply a dirt or wear decal. This is generally a game engine fix. Another option is to simply scale the uv on a cleaner tiled map. I test tiling quality in photoshop and define a pattern off the swatch to see how good the tile is I am using. Another trick on some things such as bark I skew the uv and it causes a spiraling or wrapping pattern to break up the tiling on my trees.