Building a Case for a Serpent, Part I

In order to attempt longer and more adventurous Snake On A Bike journeys, I want to build a better case for Charlie the Serpent. The existing case is a box, lined with blue muppet pelt, with some padding on the two largest sides. But there's nothing that really holds the instrument securely within the box, it is very heavy, and the box itself is worryingly flexible. It has all the weight of a...