ash
using the front draft door opening works very well for me.
I keep a 33 gallon trash bag in the cart. I do not open all the way into a bag, I open it 'til it is a double thick plastic sheet, slide it under the front of the cooker so several inches are beneath the front of the cooker.
Use a paint brush to sweep the ash clear from inside, brush off the outside of the draft opening, slide the bag out, pick up the four corners and deposit the ash in the back of the flower garden. Fold the bag into quarters and store in the cart.
Putting a hole in the bottom of the cooker would present another opportunity for unwanted air flow, maybe structural implications and as FM pointed out, possibly obstruction by small bits of lump.