Ah I see, that is what the mask if for - going on the ferry.
I'd been planning on riding the Chilterns Cycleway this weekend but the chance of getting rained on has put me off, and this looks like the best window for good weather for solstice weekend. I'll definitely try make it.
For the way out, to keep it flat, main roads for the first twenty kms.
Should be quiet though.
I am going to bring a face mask, maybe it woud be possible to catch the Tilbury Ferry on the way back and come up through Rainham.
https://www.bikemap.net/en/r/6404960