IMPORTANT

The older versions of the motorcycles have a different headlights housing from the newer models.
There are two different cover models, one specific to each version of the motorcycle so please check which one applies to your version by inspecting the original covers:

OLDER VERSION (MODEL A)
The original cover has 4 locks on the base and the rubber seal can be easily removed from the cover.

NEWER VERSION (MODEL B)
The original cover has only 3 locks on the base, the seal is glued to the cover and there's a wide bar on the top side.

A while ago I bought a LED H7 lamp for my BMW F800R but it includes a big heatsink on the back that prevents it from fitting inside the original high beam headlight housing.

After searching for a while I found this thing that was pretty close to what I was looking for but not the exact design I wanted.
I was inspired by it but decided to design one from scratch with a more elaborate profile that allows for a better grip.

My F800R is the 2011 version so I'm using model A of the covers.
The low beam original cover is big enough to fit the LED with the heatsink but it needs to be forced a little bit and there's no room for the fan to breathe.
The high beam doesn't fit at all so I designed covers for both high and low beams.
There should be about 1cm of space between the fan and the back of the cover in both cases to allow for proper fan beathing.

I kept the original rubber seals, they work pretty well with the custom covers and provide a tight seal just like the original covers.
For model B the original rubber seals are not removable and so I got a piece of foam similar to neoprene with glue on one of the sides that can be cut to fit and works well as a seal.
You can use other materials as a seal, but keep in mind that for model B it needs to be a little bit elastic and also the right size/thinkness to create pressure and secure the cover in place, otherwise the cover will not hold/lock in place.
You might need to adjust the headlight case all the way to the front if your suspension is hitting the back of the cases when full turning right or left.

Both BMW F800GS and F800R models use the same headlight housing so these covers work for both.
F1200GS use a different cover size from the F800 models, and both high and low beam are the same size.

I 3D printed the covers using PLA and have been using them for some months now without any problems.
These models have at least more then a dozen copies already riding around without any complaints, so they already had a good level of testing.
It took around 9 hours to print the pair of covers with 0.2mm layer height and supports.

MATERIAL UPDATE
So after around one and a half to two years time with continuous use the PLA starts to warp and looses the tight fit leading to some covers falling off.
Not completely unexpected I guess, PLA is not good for outdoor use.
Go for PETG for a long term solution.

The LEDs themselves (55W each) are pretty good, provide a better visibility than the traditional H7s and they are fast enough to use as high beam flash (pass).
They are easy to find online for around 25€ a pair.

LED UPDATE
The price for these LED dropped over time, you can now find these for less than 20€ a pair.

Some versions of the LEDs don't have the heatsink on the back and instead have a square box on the wires - those will not work with these covers.