tarmac = UK english
B road = UK english

Ortlieb is the best

Personally, I do what you do and find a backpack much easier for a multimodal.

Some days, I cycle into work and catch the train to airport and fly to the continent. Much easier with a backpack than a pannier.

But, by jove, carry on as you were before my interlude!

FYI: I use this and it shows no appreciable wear after 500 days commuting, 100 train trips and probably 100 flights (or 3 years of daily usage).

the journeyman traveller: Arc'teryx Spear 20