So the place I hunt had a fiberglass blind that was in pretty good shape besides the floor being a little soft. So we took the blind off the base and trying to figure out a good way to bond the old fiberglass walls to a new piece of marine grade plywood as the floor. Anyone have experience with this.

Can you provide pics? One way would be to sandwich the existing floor between two pieces of plywood.

Yes, it is a hellofa job to do right. Unless you have experience & equipment like would be used to build one.

Cut marine plywood slightly smaller than walls, like 1/8".
Put 2 - 3 layers of fiberglass mat & resin on plywood. Allow to dry / cure.
Should end up being a tight fit into the blind walls.

Rough up inside & outside of blind walls about 6" - 10" up from bottom. 80 -100 grit sand paper.
Set blind over encapsulated plywood, use at least 4 6" wide x 12" long strips of resin & mat on outside to hold blind to plywood.
Allow to dry/cure.
Start on inside and lay 2 - 3 layers of mat & resin to bond walls to floor extending at least 6" up walls & onto floor.
Allow to dry / cure.
Then lay 2 layers on outside, first layer 6 - 8" up walls & floor, Second layer about 1" to 2" further over the first layer.

I've seen people just glass in the new floor from the outside with 2 layers then use a bunch of epoxy for bonding the floor to walls on inside.

Frame the plywood on each edge with a treated 2"x4" by the length per side. Put the narrow end down and attach it to the plywood then slide the floor inside the blind. I would drill the blind walls first then attach the blind to the 2x4's with stainless steel screws. If your corners are a bit rounded I would stop the 2x4's a little short then caulk the corners well. I would cover the floor with carpeting also. I would make sure to the fiberglass walls extend past the floor edges. I would probably caulk the outside bottom edge all the way around the floor to seal it better.