OK, I finally took the time to explore this site some more and answered my own questions.
Gulfstream replaced the lower bunk mattress on our unit about a year ago under warranty. Same mattress so I don't see it lasting any longer than the last one. Our daughter uses it as a step to get to the top bunk which really puts a strain on the corner of the mattress where she always steps. We have one more extended weekend to take in October then, we too, will put her to sleep for the winter. Happy trails!