70l roll up bag on the back of a CB500F

[motchen]

Hi there,

I have been planning a trip from London, UK, to somewhere on Great Britain this summer (given the pandemic I won't be going much further it seems). I am planning to do it on a CB500F, which obviously lacks anywhere for luggage. I have a 70l waterproof roll up bag which I have been using to carry some stuff to work on Mondays and home again on Fridays.

I strap it on to the back seat using ROK straps. It has a giant velcro thing on the bottom that I only recently discovered so now I'm wondering if I can strap that under the rear seat as well. It feels sturdy.

Since I live in London I never get over 20mph using this setup. I was wondering if this would be safe for long days on a motorway and for going down countryside lanes? The way it changes the handling on my bike is already very noticeable in London. Would that be exaggerated at higher speeds and on twisty roads?

Cheers!