Bought the Caboose ultralight, as well as the additional seat to fit my 19 month old and newborn (with the car seat attachment). Made sure to purchase the rain cover as I wanted the convenience of having a cover that fit the specific stroller I was buying rather than a third party seller. However, silly me I didn't factor in that not many people use the car seat attachment, which means the rain cover unfortunately did not fit over my stroller at the moment.
It will work fine when our youngest is no longer in a car seat though, so a third party rain cover will have to do at the moment. However I wish there had been a mention (although now that I think about it, it is quite obvious that it would not fit).