havnt made any little boxes with a 45 degree router bit but have made couple chest tha thad mitrd corners..you will need to watch for tearout and use a miter guage with clamp to hold your piecer secure..hand pressure wont get it and yu can have a miscue,,not good try making a sled for your mitre slot with some fine sandpaper to help in the holding. use a clamp if yu can on your sled.. do your end cuts with a backer board, to elimate the chip out on the exit.. can do a precut as well on the tsaw to help the router work out.
If in Doubt, Build it Stout!
One hand washes the other!
Don't put off today till tomorrow!