Printing

I printed these in white PETG at 0.2 mm for both the mount and diffuser and it works great. The diffuser is printed flat, and it's thin enough to bend into the curve that's shown.

I tried transparent PETG for the diffuser, but it's too transparent.

Mounting to the Wall

I mounted them by using 3M command strips.

Connecting Multiple Strips

I didn't need to do anything special to join adjacent mounts because the diffusers and LED strips themselves hold the mounts together. See the detailed steps below for how that works.

Corner Mounts

Depending on which way you want your mounts to sit, you have a couple of options. In this model, I've got a 45° mount designed for it you have the lights flat against the wall. There's also this remix by Dave Strider that gives you a corner that's suitable if you're mounting into the corner of 2 walls (or a wall & ceiling).

Detailed Steps

Step 1: First Mount with Short Diffuser

Attach one side of the first mount to the wall with two 3M command strips on just one side of the angled part of the mount. I only put the strips on one side because wall corners aren't exactly 90°. If you try to attach to both sides of the corner, it will stretch or squeeze the mount because your walls are probably not perfectly square or straight.

Feed the LED strip into the slot on the mount.

Use the short diffuser on the first mount. This will leave a 25mm space that will be filled by the diffuser on the next mount. Having the diffusers span the gap between adjacent mounts makes it easier to have no gap between adjacent diffusers.

Step 2: Next Mount with Normal Diffuser

Mount the next strip and try to align the slots for the diffuser as closely as you can with the first strip. 

Feed the LED strip into the slot on this next mount.

Finally, slide the normal size diffuser on the new strip and carefully feed it into the slot for the first strip. This requires some patience. I had the best success when I pulled on the top and pushed at the bottom of the diffuser. Also make sure the slots are aligned well between the adjacent mounts.

Repeat step 2 until you get to the last mount.

Step 3: Last Mount with Long Diffuser

The diffuser that's on the previous mount on the wall will be 25 mm short (because of the short diffuser that was used on the first mount). For the last mount, use the long diffuser which will fill in that 25 mm gap and go to the end of the last mount.

Changing Parameters

You can change all the parameters for this mount in Fusion 360 under Modify > Change Parameters. I set the angle of the sides to 135° to fit in a corner, but you can adjust this. Things start to go weird if you get too close to 90° – I may revise the design to handle this better.

These work well with the WS2812B strips I have