Why do you feel the need to control the box? If it is going through a pre-programmed sequence then just let it do the sequence. LEFT, RIGHT, TAIL, BRAKE.
Of course you do need to think about the sequence a little bit. Common errors in wiring might include swapping left and right so your guys using the box need to be accustomed to always seeing LEFT first. Maybe go: OFF TAIL LEFT RIGHT BRAKE BRAKE+TAIL. By including some deliberate off time, you can identify the start of the sequence.
The hardest part is going to be building it into a box which is both rugged and portable. But not so portable that it leaves the site.