This was the one I found that works well. Not a tight fit and ample padding. https://www.amazon.com/dp/B079ZYRM58?ref=ppx_pop_mob_ap_share Update: I have the 15 in version.
My RB15 is currently using a Tomtoc 360 sleeve (the one for an XPS15) and it fits great in it. Well padded on the inside and along the edges. The power adapter is bit bulky to try and stuff in the pocket on the front of the sleeve, but that is usually in my bag in a separate area.
Here is the amazon link: https://www.amazon.com/gp/product/B079ZYRM58/ref=oh_aui_detailpage_o02_s00?ie=UTF8&th=1
https://www.amazon.com/gp/product/B079ZYRM58/
This fit both an advanced and base model when i tried them in 2020. Became the sleeve for the thinkpad and is very well padded.
I use this tomtoc one from Amazon for a 15 base 2020. https://www.amazon.com/dp/B079ZYRM58
The advanced model is 2mm thinner, but length and width dimensions are the same.
I bought this one (same model but from amazon Japan) about 3 months ago :
https://www.amazon.com/dp/B079ZYRM58/
It fits perfectly, as the XPS15 has almost the same dimensions...
It's well padded inside and has worked fine for me so far.
Double check the dimensions before buying though, as this is not the exact link I used (different shop, same model though).
buy the 2018 skin, and just slightly expand the area for the Ethernet port on the bottom skin with scissors, everything else fits the same. all that was done in change of design was moving the ports on the left forward for the larger power port.
I have this sleeve and like it, fits base and advanced: https://www.amazon.com/tomtoc-Protective-Compatible-Shockproof-CornerArmor/dp/B079ZYRM58/ref=sr_1_4?keywords=tomtoc+xps+15&qid=1573581786&sr=8-4
u/alcadian recommended in another thread titled: "Case for 15” Razer Blade (2018)", to use this case: https://www.amazon.com/gp/product/B079ZYRM58/ref=oh_aui_detailpage_o02_s00?ie=UTF8&th=1. I took his advice, and bought it. It fit like a glove and was super protective for my 15.6" (in the 15" size). I would totally recommend it to anyone looking for a blade 15 case, as long as yours is also 15.6".