I fill them as normal, but I put them on wheeled carts that are specially made for large planters.

I turn a plastic pot upside down and put in the bottom of the larger pot and fill around it with packing peanuts. Works great and helps with drainage.

I to have put a pot upside down within the larger pot. I cannot comment on the packing peanuts.

Packing peanuts have worked for me. The only problem is that if you want to empty your pots and re-use the potting soil, you have to pick the packing peanuts out of the dirt because it all mixes together to some extent. ... I use soda cans, yogurt containers, even juice bottles in the bottom of my pots.

Late to the conversation, but...

I use packing peanuts, but I contain them inside plastic shopping bags, like the ones Target insists on foisting on us. Fill the bag 2/3 of the way, tie it shut, and tuck it into the bottom of the pot. It's much easier to clean up at the end of the season!