Patching sagging floor

[jacobus arminius]

After hurricane Katrina (yes, my 20 year old MH survived 130 MPH winds!), although we tried to prevent it, my deep freeze leaked onto the floor. It has caused probably 20-30 sq ft of damage to the flooring. It is confined to a few spots, but I feel it would be wise to extend it to the 20-30 sq ft to strengthen it and avoid future problems.
My question is this: do I add any 2X4 bracing between the joists to help support the patches? How do I simply replace this section of flooring without having to redo the whole room?
Thanks

[Mitch Vierra]

I always have. I make in a H pattern makes them "easy" to install.