I made my own case for the receiver with a small utility box from BassPro. The transmitter and its battery just get bound together with bubble wrap and electrical tape and placed in a nosecone payload tube.
I mounted my transmitter and 1S battery on a small piece of 1/8" ply. It fits in a small, about 38mm tube, that I made end caps for. I tape the end caps on and tape the tube to the shock cord with electrical tape. (buy 8 roll packs from Harbor Freight for cheap). I also started using 54mm tubes inside my 3" and larger nose cones and a couple of "wider extensions that attach on to the original board so they slip into the nose cone tubes.
Ironically, my largest 6" rocket still uses the small tube taped to the shock cord.
Either way, it's easy to remove and charge and put in the next rocket.