I've had my Raspberry Pi 3 B+ for about a year and couldn't find a good project for it until I stumbled on to a Pi Lunchbox Laptop idea on Instructables. I liked the basic concept but knew I could improve on it. I decided to place the Pi behind the screen and mount it that way which gave me a lot more room inside to put the battery.
The battery bank was a bit of an issue but (although I haven't tried it out yet) the 10,000 mAh bank should provide sufficient power for the pi and screen. The only downside is that the bank will have to be charged between uses but it is a better design than using the Pi battery chord that came with the kit. There was just no place to put it.