I am using a hail cover made by HP Autozubehör
https://www.hp-autozubehoer.com/prod...eel_covers.htm
Amazon:
https://www.amazon.co.uk/Hail-Protec...7SX4NYH0D1D9A7
It is the XL size (533cm x 177 x 120) and it just about fits the G12, I would expect a better fit on the G11 though.
It comes with two straps which I feed through the alloys, bit of a pain to grab the clip but it seems to hold the cover lower down and better than going through the wheel arch. It helps stop the wind lifting it up.
There are two vents by the B Pillar which seem to really help release the wind pressure, however, I have found once the wind picks up to over 30mph, the two straps are not enough. So I've bought a load of tent clips and rope to stop the sides from lifting in the wind. The gap between the two straps is just too long on the G12, it would probably be fine on a 3 Series!
The clips work great, grab on to the cover and you slide the clamp shut. Quick to release too. Here is a link to the clips...
https://www.ebay.co.uk/itm/Windproof.../184313808383/
I use three ropes, clamped near the middle of the rear doors, under the wing mirrors and the third rope that is clamped on the two rear corners (by each exhaust) of the cover and wraps around the backdoor rope to create a V shape. That stops the wind lifting the rear of the cover up. I haven't added an extra rope at the front as that is right next to the garage and the wind doesn't get under it there. If exposed, I would certainly add another rope which then wraps around the rope going under the wing mirrors and attach it by each fog light.
Yes, it's a bit of a pain to set up with the extra ropes, but once the rope length is correct, it just takes a quick flick of the release botton and it's unclipped. I leave the other side clamped on.
I have added a length of pipe lagging to the back of the clip to stop any scratching, but this maybe overkill.
I went for the hail protection as it has a 4mm thick padded top, which in the event of a hail storm, should protect the car and the Sky Lounge. Rare in the UK, but not unheard of.
The extra weight of the padding helps keep the cover on when fitting in wind too. I had a really light weight cover before and that just filled up like a hot air balloon even in the slightest breeze.
All-in-all, it's not perfect, but not bad. With the extra ropes it works even better in poor conditions. If only the sides were deeper, it would make all the difference as the wind would struggle to get under it. I only paid £50 inc postage from a chap who had never used it. So it was a punt worth taking.