250lbs is bigger than a suitcase, but the design is still feasible and simple. And it's small enough to move around, even if it was 500lbs. Hell, I have a gun safe that's nearly 1000lbs and it's been moved by 2 guys and a dolly!
If a nuke is going to be used against the United States, I expect it to be smuggled onto a freighter and detonated in once in port long before it is ever unloaded.
Bet they didn't glow when they were done /s