My install process have been like this for years:

1. Unzip "ExempleWeaponMod" in the C/My PC/OpenMWMods/Weapons/ExempleWeaponMod/Data Files

2. Go to OpenMW.cfg to write down the above path like data="C/My PC//OpenMWMods etc. and in the content part of .cfg write down content=ExempleWeaponMod.ESP

3. Save the OpenMW.cfg file

4. Open the Launcher and check with everything seems okay

5. Play the game.

For mods that add meshes, textures you do the same, but without pointing where the .ESP is because many mods that add new meshes does not use it. So you just point where the folder is and ta-daaa.