With your kits unplugged, place them facing opposite short edges of the tin and mark where the ports need access.
"Dry fit" the unplugged kits to see that they fit in the slots you snipped.
Use more foam tape or regular double-stick tape to secure the solar charging circuit, and plug the MintyBoost's JST cable into the LOAD port on the charging board.
Plug the battery in to the BATT port on the charging board, and use more double stick tape to secure the battery on top of the MintyBoost.
Remember that we earlier lined the tin with tape and wrapped the battery in tape as well!