I keep an archive of MUI 3.8
here which is intended to update an existing package, but can just as easily be used to install a full MUI setup with the latest versions of all the relevant custom classes for nearly everything.
For a first time install, you'll need to add some some assigns and stuff to S:user-startup, all the information you need is in the included readme.
Just follow through all the steps in order and it should work.
I'm too lazy to write an installer script, but I'll do it if I get really bored one day.
Demo keyfiles are included which means you can't save an edited config, but at least this will get you going.
You can still register MUI which will get you personal keyfiles.
Else if you buy a CD of OS3.9, you get the Genesis/AmiTCP as part of it.
You'll still probably need MUI in the long run, a lot of apps use it.