My floors in both my bathrooms in my mobile are completely caving in. I cannot afford to pay someone to come and fix them, and all the web sites I've checked out only tell me how to put new plywood over the pre existing floor. If my floors are almost gone how can I achieve this goal? I just want to know how to lay down brand new plywood but I need a step by step guide on how to do it. Where can I find this kind of guide for free?

I don't think anyone is going to be able to give you step by step instructions. For one thing we are not there and cannot see just what needs to be done. For another, I and most posters on this site are probably not familiar enough with mobile home construction to to do that site unseen. How ever general guidance would be to remove the toilet and vanity, cut out all the damage plywood. Inspect the supporting members for damage and rot. Inspect the plywood under the tub area and decide if it also needs to be removed.

Do any repair or replacement of the floor joist. Sister on any necessary 2 X material to restore the joist. Use treated material to minimise further damage.

After making structural repairs, lay down or install a new plywood flooring. Personally I would use treated plywood. There will be lots of people rasing objections to that concept because of off gasing. In my opinion, given the amount of material being used, and the fact that the plywood will be covered by the floor covering the amount of off gasing will be unmeasurable.

Nothing complicated here, just handyman work. Important part is to do adequate repairs of floor joist.

Harold is right on several levels, we can't give all the details without being on site. The original floor was plywood sheets and does not stop at each wall of each room. The entire home was floor sheeted before the wall went in. You will be doing a lot of slicing. I would drill a small hole in each corner of the room, go benearth the home and see where theses hole match up with supports beams inder neath. You need to catch support all along the edge of the new ply.

How do I replace the weakened board under the bathtub that cracked and gave way to where I went under the bathtub

How do I replace a bathroom floor in a mobile home. The bathtub has two cracks and also needs to be replaced as I went through the weakened pressboard the put in when they manufactured it