Acceptable to bring stadium/trail chair for use in Box seats?

[gachapon 0]

 

Something like these... would I be able to get into the arena and use it in a Box seat?

[Akinomaki 24,014]

That's basically just your personal zabuton - these are allowed. You only have to take care not to block the view of those in the boxes behind you, which is guaranteed if the thing is not much wider and higher than your shoulders while sitting.