The standard advice in these threads is to check the decking first, and it's right. What I'd add is where to check, because people tend to either panic and assume the whole floor is gone, or walk the middle of the living room, decide it feels solid, and order material.
Neither is usually the truth. In the manufactured homes we work in around Willis and Splendora, the failures are almost always local and they're almost always in the same four places: under the toilet, at the tub apron, around the water heater, and just inside the exterior door that gets the most weather. That's where water has had a slow, unglamorous decade to do its work.
Everywhere else the decking is frequently fine.
Why it matters more here than in a site-built house is what the material does when it gets wet. Particleboard isn't plywood — it's compressed wood fibre with adhesive, and once it swells it doesn't recover and it will no longer hold a fastener. That last part is what catches installers out. A floor can feel acceptable underfoot and still have zero grip left for tack strip or transition screws, so the new floor goes down fine and then releases at the edges within a year.
Test it with something narrow and pointed rather than by feel. If a screwdriver goes into the decking with light hand pressure, that section is done and no amount of new flooring on top improves it. Cut it out, replace with proper underlayment, and lay over sound material.
The reason I'd rather find this at the estimate than on install day is purely financial: it's a couple of sheets of underlayment and an hour when it's planned, and it's a change order plus a crew standing in your driveway when it isn't. Any quote on a manufactured home that doesn't mention the decking was written by someone who didn't look.
If you're weighing what to put down afterward, waterproof luxury vinyl plank is nearly always the answer in these homes, for reasons that have more to do with the structure than the material.
