While others will have some very helpful ideas, I will give you my lazy answer....use the factory plastic clam shell blister! The work is already done for you. Here are a couple of mine using Greenlight, Johnny Lightning and Hot Wheels blisters carefully cut around the bottom 3 edges and reattached with tape.
Hope this is a start and some small help. By the way, they are really not warped as they appear, it's just distortion from my cheap camera.