You will need support to help you. You have zero access to the root files so uploading files for adsense isn't possible unless you go the HTMl route with an HTML widget.
@shawnlutzko did you manage to resolve this? I'm having the same issue and dont want to have to move the site elsewhere.
This has been on the idea board for a while. I recommend that anyone who is interested vote up this feature request. https://ideas.duda.co/forums/930658-duda-idea-board/suggestions/41073523-upload-ads-txt-to-the-root-of-the-site