We used to use sheetrock to many years ago, but now it is hard to find sheetrock that doesn't have some sort of additive, the sheetrock is high in calcium and will cause red urine. I have not used it in years because of that. We have learned sore hocks is more of a bacterial infection in the foot, using antibiotic creme is the best, but once the infection is healed though using something like for baby's bottoms will help keep it sealed same as the liquid bandage. Since bandaging a rabbit's foot is a joke. They will eat faster then anything.
As for rabbits with no nest box, that is fine if you have a solid bottom cage. If you have wire, you will likely loose the babies. Depending on breeds, for Flemish, I used dog crates with a piece of wood across the front to keep babies and nesting material in. But if your nest box smells like another doe or another animal your rabbits would not like to use it. I also bleach mine out, then when I place it in on Day 28 I take a q-tip dipped in vanilla extract and line the box with it lightly then rub a little on the does nose so the does smell the same smell. (Works for fosters too, then rub some of the fosters mom's nesting materials on the new baby).
There are always more than one way to handle things, I have some things work for me and some things don't. Ya kinda have to try things and see what works for you.
As for a doe mounting a buck, way common!! She is just in full cycle.
You have to be careful though because sometimes a doe can be very aggressive and intimidate your buck and he won't breed. If I have a young buck with a doe like that, I hold her. Or be sure to only used an experienced buck with a doe like that.
They did get it finished after a while and I put her away quickly so she didn't hurt him or something - but what could have caused that? I've never seen it before lol
