I think they may do a lifetime on the SS ones but not the regular steel black ones. I had those on my last truck and they rusted from the inside out. I think water got inside them. They lasted about 5 years. For the price id try them again but id try to coat the inside by pouring paint into them sealing the ends and giving a good shake. Then id consider bedliner pain on the outside. Or just stick with the stainless if you like the shiny look. My current ones were just the cheap SS off of ebay. So far they are great. Ill bump this thread 5 years from now to let you know how well they hold up.
Big Bully 3.5" were stainless but have now been line-X'ed.
We also just installed a set of smittybuilts on the neighbors Titan and they seemed designed to sit lower which works out well for the one legged *******. I can tell you the quality of the smittybuilts seems better than bully's but they didn't have a 3.5".