This may be an option except transferring a gun to and from the box at work might be a ballet that attracts attention.
https://www.stashvault.com/secret-compartment-motorcycle-floorboards/
I ride a bike too. Up until recently I had a CCW (CHL) in Oregon. I now live in California. I kept a gun in my lockable saddle bags at work and transferred the gun when leaving work but I had a parking spot where no one would really think much of what I was doing. I was kind of out of sight. When I rode my cruiser I kept the gun in a saddle bag but it was unlocked, but we had secure parking.
There really is no perfect option.
I am thinking for your situation a swing arm type bag/box. If you keep your lunch or something you need to carry into work in the bag then kneeling down to retrieve it while transferring your gun would look fairly normal...maybe?