1992 Caviler mobile home

I'm not sure if this is the right place but I recently bought this 1992 mobile home, the 30 year old waterheater was leaking, rotting the floor. The old one was a 19 gallon, the new one is a 20. I'm trying to keep the same power draw etc as the wiring for half the trailer is shot. Anyways the question i had was about the floor joists in the last picture I believe. The boards look fine but if I wanted to add support what would be the best route to take? I was thinking about screwing sister 2xs on the north and south side then taking joists hangers and adding a beam across the center to make a H, then laying the new plywood down. Full disclosure i have no clue what I'm doing, just winging it. Thank you for any advice in advance!! I'll most likely go ahead and replace the drywall and throw some killz on it as well.