Try creating a rectangle mask that surrounds your text, then merge your text with it via a merge node set to mask. Then add a transform node between the text and the merge node, and animate it.
If that’s a bit too complex to understand, I can create a demo natron file showing how it would work.
I’ve given that a try, and I can get the text to move, but I’m having trouble with the merge node and masking it - whatever I do I can’t get the text to display at all (even if I delete the rectangle mask) - I think my problem is the merge node.
If you could create a demo file that would be an amazing help, thank you!