I'm guessing you tried using the trainer in campaign mode, right? Unfortunately, the trainer increases levels only in skirmish, not campaign. Use the Wargear mod on the trainer page of this site so you can get all the wargear and then sell a bunch of it to increase your level. That's the only way I can think of that would increase your level quickly in campaign mode.
Here's a link to the mod in case you didn't know what I was talking about: www.cheathappens.com/show_download.asp?ID=25185