Try the following, it may be what you want to achieve:
1. Create a new blank drawing with only two layers (say 0 and 'hatches').
2. Select Layer 0 and draw your rectangle.
3. Change to Layer 'hatches' then select your rectangle (check that the active layer is still 'hatches' - it will be highlighted)
4. Choose Hatch, I chose honeycomb but hopefully any hatch pattern or fill will work.
You should now be able to turn the visibility of the 'hatches' layer on and off at this point. Ensure it is on (I am not certain if this is important).
5. Save the file with a suitable name (I chose RectHatch.dxf)
6. Restart LibreCAD so you have a default document (I think you were looking at templates in another thread which may be your default and is why I suggested only two layers for the blank drawing in step 1.)
7. Select Layer 0 then from the file menu choose Import/Block and select the file you saved at step 5.
This will allow you to place a number of rectangles into your (new) drawing file, and yes they will appear empty.
You should now see the (new) drawing file has a new layer called 'hatches' (or whatever you chose as the hatch layer name).
8. Select all your inserted rectangles and Explode them (from the Modify toolbar).
9. You should now be able to turn visibility of the 'hatches' layer on and off to show or hide the block hatches. You will also be able to delete individual hatches but those that have been imported are 'fragile' so don't try to modify their properties.
If you want to change them simply delete and replace with new hatches created on the appropriate layer.
Hope that was what you wanted.
If you want the blocks available through the Block List you will need to create a subdirectory in the LibreCAD Library directory (the location of which and access to will depend on your operating system).
Hi again Rick,
The previous reply may have been a more rigid approach than you required and you may have discovered that in the case you describe it is only necessary to explode the block to allow you to turn your hatches on and off.
I have done a little more experimentation and found that if you use the "From Scratch" method as described in the wiki, the hatches layer (and hence the hatches themselves) are not saved with the rectangle when you use the save button in the block list. This may have been the source of your frustration. If that is the case then try my original suggestion which does save the hatches layer as part of the .dxf file that can then be used as a block.
Thanks for asking the question. I have learned a lot in trying to answer it.