Does anyone here cover their cake and board in fondant with the cake on the board so both get covered together? 

I have an 8” round cake going on a 10” round cake drum. Both to be covered in the same colour fondant. I’m sure I remember seeing a tutorial where someone’s did this. 

if there's a bottom border on the cake I would cover them separately meself

I would cover separately mainly because when the cake is cut and served the server would need to also cut along the bottom so that the slice comes out cleanly without pulling away the cake board fondant.

I tried it. It looks ok, but I don’t think I’d do it this way again. I didn’t think about how to cut the cake. Probably wasn’t the best idea. 

I've never done it, but I've seen it done and it looks very impressive and reportedly, not difficult to do.  Good tip on the serving!

I’ve done this a couple of times, but no good pics to show you. I googled, and like you, cannot find a tutorial. I think may have been shown this technique in a fondant class I took quite a long time ago.  That’s where I got my idea from.  I covered a cake with chocolate mmf, and brought the fondant to the edge of the board and the ruffled fondant so fondant was just over the edge of the board. Cake was quite round, one tier and fondant was thick. And I did a red fondant covered cake where I took the fondant to the board edge, and used the tines of a fork to imprint the fondant. I remember it took quite a bit of measuring to make sure I’d have enough fondant to cover both cake + board with excess, in case. Then after applying fondant, adjusting the  draping fondant and smoothing, smoothing very, very  slowly so the fondant wouldn’t tear. I sorta remember it being labour intensive, and that’s probably why I never did it again. 

I never thought to do that but as I'm reading the replies here I thought about the servings and any cake under the top tier will have NO ICING :(  That could be as many as 20 servings ........not good.