and airborne at the same time?
Sorry, I could not resist. Other parts of the world would refer to this as "bonding" but no disrespect intended.
The carrying of "jerry cans" is done in Canada, but it's not talked about too much! All of the safety concerns and risks are are self evident. I can't speak to local legality, but sometimes you gotta do what you've gotta do!
Tie them down well, and in contact electically (bonded) to the primary structure. There is Canadian guidance material on cabin tanks, I can dig it up for you if it would help...