Our first housing was hutches four feet off the ground with hardware mesh floors. We had two males and one female (long story) and each portion was 18" x 4'. Our vet told us, before we figured out our rabbit died from wry neck, that she might have had heat stroke, so we moved the hutches from the yard space into our chicken house and built in solid floors. We have a small a/c in the house for really hot weather. Since we went almost two years without losing another adult, we figured we were fine on the housing end. We clean them out three times a week and use pdz in them.
After reading through this, the other girl who died recently could have cocci because we found out our daughter was putting the rabbits down in the deep litter bedding of the chicken house and letting them dig through it. Teenagers ... ugh.
But the one who's refused to get pregnant and knowing where we got the starter buns from makes me really think its the genetics of the stock.
I don't know that I want to delve in deeper with housing set ups where we live now, though since we are actively trying to buy some land and move.