Campaigns most certainly do work with TF3.00.
Installation of campaigns should be the same as installing normally- the main campaign files go in
C:\Program Files(x86)\Steam\SteamApps\common\il-2 sturmovik cliffs of dover\parts\bob\mission\campaign\
Edit campaign ini as required. -(I suspect this is the step that's going wrong- it usually is).
Infact if you look in the file locations you should see the previously installed campaign files there
The 'Mydocs/.../MODS' location requires a folder with the correct name of the campaign in it (to store campaign progress) - copying the folder you pasted into previous location works
(then delete all files in it if you wish- a new state file is generated whenever you start a new campaign).
One question springs to mind- Did you make a backup before (presumably doing a file validition). Steam's file validation is 'mildly annoying':
in that it resets the campaign.ini- ie wipes knowledge of any campaigns by the game.
Single players should keep a backup of this 'campaign.ini' file
(and it's always a good habit to make a complete backup before making any changes to any game