After performing some testing, this is what I have learned:
MapInstall 4.0.4 will work fine with BaseCamp 4.7 installed. It just needs to be installed after BaseCamp 4.7 because...
BaseCamp 4.7 installs MapInstall 4.2. It doesn't update the Windows program list with uninstaller details for MapInstall 4.2. The only way to get rid of 4.2 is to delete the "C:\Program Files (x86)\Garmin\MapInstall" directory. (The BaseCamp 4.7 installer doesn't update any registry information for MapInstall 4.2).
MapInstall 4.2 standalone installer does update the Windows program list with uninstaller details BUT it does not delete any files when the uninstaller is run. You must run the uninstaller to remove registry details then manually delete the "C:\Program Files (x86)\Garmin\MapInstall" directory. If you only delete the directory, the 4.0.4 installer throws an error when it sees the 4.2 registry values.
To roll back to 4.0.4 from 4.2:
1) Open the Windows program list and look for Garmin MapInstall 4.2. If it's there, run the uninstaller.
2) Delete the "C:\Program Files (x86)\Garmin\MapInstall" directory.
3) Run MapInstall 4.0.4 installer.