If anyone is interested (or still plays this game), I have figured out a workaround for the trainer so that you can still use it (kind of) without it being detected (kind of) and not having acheivements and progress saved.
Start up your game as per usual (trainer, game, F1, Num3, start map). The trick here is that you only press Num1 (for 10,000 res) JUST BEFORE A CHECKPOINT. If you have used this trainer before, you notice that your resources are not increased until you spend some. Therefore, if you use the cheat just before a save, your resources are not increased and the game doesn’t notice that you’ve cheated. However, in the next wave, as soon as you start to build / spend resources, you will be granted the extra resources.
The problem with this is, that when you finish the next wave, it will detect that you cheated, so each time you use the cheat (and AFTER it has saved), you need to exit back to the main menu and load up your game again. It only takes a few seconds to do this.
The disadvantage of this method is that you can only get 10,000 resources every 3 levels (each checkpoint), but it will still let you get achievements and progress through the single-player campaign. I have noticed that 10,000 every few levels is more than enough to kick monster butt.