The 5ers basement is also much much larger than the pass thru in a tt.
Here are some basement pics.
Looking at the image below you will see 3 doors on the side in the front. The tall skinny one is where the propane is housed, the large middle door is the basement. The basement frequently has an access door from each side of the trailer and the front of the 5er.
Now let's look at the little pass thru in a tt where that is literally all its good for.