Decided to go for the Lowepro Droneguard BP 450 aw. Well I really like it, everything fits in, it's really well made and well thought out. I can fit the P4, all usual accessories and the dji Osmo and all its accessories too. I couldn't be bothered to make the pics work with the forum so here's a crappy key burn video I've put together instead.

I'm impressed by its long name, not sure why it means

Well Lowepro = brand name, Droneguard = sub brand, 450 probably something to do with the level of protection or something. AW is the waterproof cover that folds away. You're welcome :-P