We have an inexpensive freestanding popup privacy shelter, it's OK but not great in wind. Something roof mounted would be nice.
I have more often just used the camp shower with no shelter, easy when you're a long ways from anyone else. We have a Nemo pump up shower and it works pretty well, better pressure if you put it on the vehicle roof.
For a ground pad, we have one of these Nemo Clovers and I like it. Unfortunately it looks like they may be discontinued, I can't find any retailers showing it in stock. It's just a silicone pad that folds into 1/4ths and fits in the shower carry bag. It's fairly small but is just big enough to keep you out of the mud.