An excellent description of a common issue. Number plate mounting tape is ideal for the task, again use double thickness as it will compress over time.
Keep trying and I'm sure you'll suceed. I just shoved it on the same way I took it off and it was quite a few years ago, plus I don't have a Smartie anymore 😔so can't really advise any further. Good luck.
Haven't had any problems with the internal handle so can't help with that but check out www.evolution.co.uk as there's a wealth of information on that site.