You can use any kind of a small metal box made for electrical installations - you can buy "bell" boxes, which are cast aluminum, or stamped steel boxes. Both are available with blank covers. The ignitor doesn't need to be with the ballast, it is just more convenient to build the ballast with it there. Ignitors are rated by distance, and if you exceed their limits, they need to be moved out to the hood.
to remote mount the starter you need to use 4 conductor cable and to do it correctly the cable should be 105c/ 600v
Wow that is some ridiculously unsafe advice...must be boredom forcing peeps to post on a dead thread. any wiring can be extended safely. cut and splice.