Plywood is the best type of subfloor for a mobile home, though if you’re installing flooring in a bathroom, you may want to install a vapor barrier or use a moisture-proof subfloor material like Amdry. OBS is similar, but it can swell when moisture is present. 

Either way, old mobile home subflooring made from particleboard can cause issues with your joints. If you’re replacing your subfloor, it’s best to upgrade to plywood.

No, squeaky floors do not always mean there is structural damage. The noise is often caused by friction from issues like loose floorboards, gaps between the subfloor and joists, or loose subflooring. While many squeaks are harmless, persistent or worsening noise could indicate a more severe problem. If you notice other signs of structural damage—such as soft or sagging floors, cracks running from the wall to the ceiling, or horizontal cracks in your foundation—it's best to have a professional inspect your floor to determine the root cause.

Dry rot or severe water damage may warrant a replacement, but you don’t always need to replace damaged subflooring. If your subfloor has warped because it was installed incorrectly, you can sometimes shim the panels (in other words, add a thin, wedge-shaped piece of wood to level the surface). If your subfloor bows upward, you may be able to sand it down at the joist so it’s level, depending on the extent of the damage.

Whether or not transition pieces go under the baseboard depends on a few different factors. If the transitions are being installed with the flooring and before the baseboards, then they will go under the baseboards. If the baseboards are already installed, then it depends on whether or not you want to remove them or undercut them. If not, the transition pieces can butt up against the baseboard.