First off... That's very innovative thinking and the mod looks sweet! You are pretty good. I noticed that you debossed the battery/board ventilation holes on the bottom. That's smart for many reasons, especially for a keeping water out when it's standing on wet surfaces.
I've been working on a custom mod in CAD software. I'm trying to design the board support and battery support/contacts right now. My goal is to provide sturdy support but also protection from drops ( I drop my mods alot 🤷) and it's a tough issue. Currently I'm researching different material properties and that's all I'll say publicly, until I figure it out at least, as to how I'm planning on achieving this. This is definitely a cool idea. I have a couple questions for you about it.
Does it cause any excess/extra heat to the battery or board since they sharing the same material for heat to dissipate onto? Did you apply any other heat release design features to the mod? Lastly, have you dropped the mod yet and how did it fair with the design you have?