*Open cell foam is generally bad for long term storage

You would be fine if you used closed cell polyethylene foam, which you can pick up at places like McMaster Carr or Amazon.

Get a Fieldline Alpha OPS internal frame backpack (~$65). Then get some kaizen foam from amazon (~$25) and make a custom shadow box to hold the phantom and accessories. You will have some extra room and many pockets for other stuff. Alternatively instead of the diy kaizen foam, get this cheapo bag from ebay and take out that foam and put it in the fieldline bag. There will be a space on top of the bag you can fit other stuff in there. The fieldline is a clone of the tactical 5.11 rush 72 hr bag which retails for $175 and every bit as good according to reviews. You can use the cheapo bag for other stuff as well, its just not very comfortable.

EDIT - words