I don't care if people notice that I've ridden my bike... It can be a sign of life, or environmental choices, and have nothing to do with poverty or DUI.
I've looked at those moped boxes before. I probably won't add one to my rack, but it should work.
A few additional thoughts:
Ortlieb Roll Top Panniers should be 100% waterproof. Not necessarily lockable, but could be good for carrying dry stuff too and from work.
I use trailers a lot for groceries and store runs. I mostly use an open top ex kiddie trailer. However, I've been thinking about my Bike Friday trailer.
I'm going to try making a similar one with a slightly larger suitcase, and flat-free tires. Hopefully ready shortly.
Another option for trailers are various storage boxes, but finding good sturdy ones cheaply seems to be a problem.
Oh, for rack boxes, Harbor Freight also has Pelican Style waterproof boxes. No lock, but provisions for a padlock.
https://www.harborfreight.com/3800-w...-in-63927.html
The boxes regularly go on sale. Find a coupon.
https://www.harborfreight.com/see_new_products.html
$29.99 with the coupon.