For my use - I find that gravity does a wonderful job of keeping the Al plate sitting nicely on the wood base. As long as you don't want to pick it up by grabbing the transformer, I don't see a need to have any kind of additional attachment.
However, if you do want to have some kind of attachment, I'd imaging a dab of silicone caulk at each corner would do the job (and is easily removed, if desired).
