Thanks for the video but I've installed many, many mods before. Currently I've installed Alexander through Steam, ran it for one turn and saved the game. Then I copied it to "C:\RSII\Alexander Total War" and I'm making copies of it for the inevitable installs I'll have to go through until I get this working.
I first tried this install of RSIII:
https://www.moddb.com/mods/roma-surr...lone-installer
The launcher said it was v3.0, not 3.1, not sure if that's relevant but when I finished the install and ran it it simply launched vanilla RTW.
I'm currently trying RSII 2.5 from here:
https://www.moddb.com/mods/roma-surr...a-surrectum-25
Should I just keep going through different installers until I find one that works ?
Thanks for the help !