I use a number of textures to help me map. Even the most seasoned mesher can find this part of meshing frustrating. I use these for different reasons and I am making them available for download if you think they might help you.
I use UVMapper. These should work in your program too. UVMapper does not recognize DDS and I personally hate that format due to a long standing history of glitches with the plug in. You can load in your multiplier, mask, overlay - whatever to help you suss out problems/solutions and is a easy way of figuring out issues prior to getting it into workshop or worse - the game.
The grid pattern is something I made prior to realizing UVMapper had one preinstalled. Mine is a smaller scale and I still prefer it. This can be helpful for scaling especially. Sometimes you need to remap an area and now it is no longer in scale with the other pieces you've previously scaled together. This can also show oddities/warped meshes (as will any of these other patterned textures) so using a texture after mapping to check details can be especially helpful.
The wood pattern is great for direction. When you have something you need the grain going a certain direction - this is ideal as a texture while you are orienting your parts. I have noticed in my own game that I have an abundance of vertical grain woods and significantly less horizontal, so I tend to map (personally) for this orientation. When using this as a check, you can quickly see what is oriented incorrectly.
The line pattern could also be used for this, but it can be visually confusing. I recently added this texture to my arsenal to assist in reshaping the legs of one of the end tables in my last set. Early on I mapped it one way and needed to have the legs reshaped. I manually moved the points using the line texture for assistance. (Then using the grid, I made sure every segment was in scale for the map).
The last texture is for more advanced mapping. When you want to have a rectangular map (vs the standard square) that is still tiled (for example) 2,2 or 4,4 or you need a pattern repeat (all patterns are 256x256) this can be handy. UVMapper is not especially helpful in this arena, so having something that broke the area into quadrants is helpful.
Hope you can find some use for these. They have saved my ass on a number of projects.