Where is this spot occurring on your hull? I had soft spots on my '79 hulls just in front of the forward pylons, and I understand that this is a common place to get them.

If it is indeed a sure-fire soft spot, you're gonna have to cut out port holes or inspection ports to air them out. That's what I did and it seems to work fine. Just make sure that you use high quality sealant, dont settle for the cheap stuff, because I could really tell the difference.

hope this helps