This was a super quick case that I made for my RPC. I noticed there were no real solutions for a case for the 6 button version. So I found the great parametric storage box that @Mihai_B_Mike made, customized it for the size of the RPC, and then made inserts for the case based on the rough dimensions of the RPC. 

This could definitely be adapted for a 4 button model, and I may do that in the future, and also, there are some little things I would like to do with the inserts, but again, this was something fast I needed before going on a trip, and it worked great. 

Based on the parametric box, you will need 2 - M3 x 30 screws to secure the hinge, and 4 - 8x3mm magnets. The magnets are really more or less a press fit and I haven't glued them in, but I think they would benefit from the extra adhesion so they don't get pulled out of place (like in one of my pictures lol). 

Would recommend making the inserts out of TPU for the extra cushion and so that harder material won't scratch your RPC.