Space under slide to add plywood to floor

I had the same problem. The soft spot was under the back corner of the slide. Right where the slide met the wall. I pulled the slide about 3/4 of the way out. I got under the slide and slid a 1'X 2' 14ga steel plate between the carpet and decking. I bought the pre-cut plate at HD. It wasn't easy but I got it in. There was a black fabric material between the decking and carpet that gave me problems. I filed the corners and edges of the plate smooth so it would slide in easier without catching on the carpet or fabric.

About a year later the floor deteriorated enough that it became a large soft spot. Even after the leak was fixed. It cost me $2800 to have it done right 12 years ago. I have no idea how much that would cost today. I do know they had to pull out the slide to fix it.

Or use a piece of plate steel. That's what I did on my boat. I just pulled back the carpet and slid the plate in, then stapled the carpet back in place.

bgum wrote:
They make an adhesive that is injected into the soft spot and hardens. Not expensive and may be best. Look on YouTube for guidance.

I think this was developed for boats, if that give you a place to start looking.
Might think about injecting from below where any mess will be hidden

They make an adhesive that is injected into the soft spot and hardens. Not expensive and may be best. Look on YouTube for guidance.