The opening is a bit rough, but it's away from the door and wide enough for the cats, so it works for me. Basically, I drilled a large hole for each of the bottom corners then used a sawzall to cut across the bottom and from the top, down the sides. Easy peasy. I didn't worry about leaving a top for the hole, as the lid to the trunk created that for me. Then I did a quick sanding to the edges so the kitties wouldn't get any splinters.
Creating a fancy litter box meant that I no longer had a trunk in the living room. I loved having it there because it also acted as a table for reading material and as a window seat for gazing out, over the summit. I have been checking thrift stores and online for months, looking for something affordable but beautiful and hadn't found anything acceptable that was in my budget.
So now the house has two trunks, both serving multiple purposes. One is beautiful, classing up our reading nook. The other is making our bedroom much, much nicer. It looks like a restful place and not just Cat Land, and when guests come over and glance in our bedroom, they won't be presented with an eyeful of litter box.