Hi I have been looking at this Air Box and trying to figure out how I can Vaccum Bag ??? to me looks impossible, so any help appreciated, Regards DM

It is exactly the same method that Easy Composites used in their first pre-preg tutorial video. Watch here from about 15 minutes in and pay attention to how they make the bag meet itself inside the mould by feeding it in from two sides:

https://www.youtube.com/watch?v=cQ1Q4XmItN0



In all honesty, I think tubes and things with a single opening on each end are best done with internal vacuum bagging methods as you described where the bag is pushed through the inside of the mould and pulled back over the outside and sealed onto itself. But for parts like this airbox where you have two openings on the one side, although you can make an internal bag work it is much trickier, and so it is just easier to use the method that Easy Composites demonstrate in the video.