We just replaced our axles. One of them was bent we discovered on our last trip, when we had a blowout. :( My dh went with much heavier axles and larger tires so that he could get a heavier duty tire.
We also just replaced the mattress in ours. We went with a futon mattress that had great reviews on Amazon instead of a RV mattress. It was less than $100. We haven't spent the night yet, but it feels great. We did lose about 2 inches in width, but felt it was a worth the trade off.
Last year we changed out the bottom bunk and the pull out for three fold out cushions from Amazon. This has been great. We can put three people in the bottom bunk space. When we are ready to travel they fold into the bunk space like a thick mattress out of the way.