I'll be taking my MSF BRC in a few days and wanted to get a solid idea of what to buy for accessories. My security will include a 13mm 6.5" Protector chain, 2 Squire SS50CS Stronghold High Security padlock, an Abus 83WP/53 Weatherproof House-Key padlock(to lock the cover), and a Dowco Weatherall Guardian Plus Cover(with cover alarm). None of which I have on hand yet, so I'm not 100% sure if I can cram it all into the underseat storage, but I sincerely doubt it.
I was considering the Honda Genuine top case, but I hear it's both pricey($275) and of poorer quality than the Givi cases, but I also hear that Givi Monolocks are simple mouldings and aren't very strong. That, and I'm wondering about security. I see a lock on the OEM case, but it doesn't look like it's screwed onto the rack in any way and can simply be popped off in seconds. Am I missing something about that?
And how big is that underseat storage? I have a Scorpion EXO-1100 Sixty-Six Neon Helmet Medium Full Face. I'd also want to stick my riding gloves inside as well, so I don't have to lug both of them around with me, and figure maybe the seat storage might be better if I'm a victim of accessory theft and they either pop off or tear off the case. I recall reading that someone had trouble getting the seat to close on the helmet and needed a separate top case because of it.
Would it also be awkward if I tried to ride with this rested on the seat while the strap on my shoulder keeps it upright?:

It would weigh about 18 lbs. I have a proper backpack, but my experience with riding a bicycle with one is that the weight is going to strain your back trying to keep yourself upright.