There are so many unanswered questions from your post.
What year is the Montana? Being a TT, it's probably an older model and I wonder if slides being relatively new, that it was weaker than the ones in the newer Montanas that don't have this caution. On my '06 there is just mention that the slides be retracted and extracted to ensure lubrication. It only cautions not to leave the slides extended while in storage. If you are living in it and almost the same as storage, the difference that is you'd be present to operate the slides for lubrication and would notice if any other slideout problem was going to occur.
How long is an extended period of time? A season, a month, a couple of weeks? What kind of support is called for? There are vertical supports sold after-market but some of us don't like the looks of these because of the potential damage to the slide or rig if a tire goes flat. Living in it as a full-timer and many owners don't operate their slides while living in them and haven't reported problems. In your model year maybe there was more to worry about.
Like everything else in a trailer, there's always something to worry about, but care, maintenance and checking should keep things working and safe.
If you are interested in supports, these are what I've seen, but have gone no further since I am not a full-timer and have never kept my slides out any longer than a couple of weeks:
http://www.rvsupplywarehouse.com/pro...l.cfm/pid/1599 (by Ultra Fab)
http://www.campingworld.com/shopping...set-of-2/11253 (by Stromberg-Carlson)
http://www.rvpartscenter.com/RV_Part...stabilizer.htm (and several offerings from SideWinder)
As for the forum, you'll find a wealth of information and even some different options. But you should get enough info to satisfy your need from actual users and members to create an option that works for you . Welcome!