Axles last 15-20 years. You would replace the entire
axle (and get brakes!) not just the torsion bars (which are rubber). Cost $250-$700 depending on whether you have the
axle shipped, you do the welding, etc.
Yes, cabinets can be added, either by
Scamp, you can order from them, or build them yourself.
We have a powerful search engine here at FiberglassRV (upper right corner of window), I'd suggest clicking the "More Search Options" to search all forums (or select a particular form), place a four-character word in the "Search by Keywords" box and you're good to go. To search for multiple words place a plus sign ahead of the word. Click "Advance Usage Help" within the Search engine for more assistance.