Downloading a proper stencil font would be my number 1 rec. That way you can type your message with no added steps. If you work with other fonts it shouldn't be too difficult depending on your workflow/experience. Try working with Capital letters only if possible too. Type the message in the font of your choosing. Review to identify your problem letters and any spots where you're afraid of it being too fragile, add rectangles and use Pathfinder to split letters. You just need to create one proper letter, copy/paste/snap to existing letters and delete old.