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After tearing out the interior we had two choices when it came down to it:

Stick with the plan, sand the floors a bit and rebuild as originally planned.

Do it right, rip the floors out and see where that takes us.

As has come a pretty constant theme of this project, we chose the second option. We plan to keep this thing for a long time and enjoy it as often as possible. As such we opted to go ahead and tear it down to the bones and see what we really got for our money.

The biggest hurdle was removing the wheel wells, they are screwd down and glued down and are fragile. This required some finesse, but at the end of the day they all came out without a hitch. The propane and generator compartments came out as well. (everything has to come out to pull the floors)

The floors were a bear as well, once again screwed down (with 40 yr old rusty screws no less) and glued down with panel bonding adhesive. Whatever GMC used is some SERIOUS stuff, and still functions exactly as intended nearly 40 years later.

Once the flooring was all pulled (once again with a lot of curse words and crow bars) this is what we were left with.

I am so glad that we pulled the floors, it exposed a few other problems that were just waiting to rear their ugly heads at some point down the road! In the first couple pictures you can see our helpers helping with the floor removal.

The first thing we noticed was the fuel lines, they were pinched and rotting and generally in terrible shape. Having the floor removed was the perfect opportunity to fix that issue. 50 ft of 3/8 fuel line later and it’s all new and ready to go another 40 years.

While working on the fuel system we also noticed that the body mounting cushions were either missing or flat as a pancake. This makes the body ride rougher on the frame, crush the fuel lines, bend in the middle etc. Bad news.
There are a few commercial options for replacements but like most things GMC they are pricey for no reason other than small production runs and limited vendors. A trip to TSC and a 4 x 8 x 3/4″ sheet of rubber solved this problem. We used a band saw to cut it into pieces the appropriate size and then used the forklift to lift the body enough to get them under the frame. Big improvement!

Now that everything under the floor was fixed it was time to take care of the actual floor. To do this we reinstalled the aluminum pieces underneath the floor, replacing the ones that had holes in them from the original plumbing. We insulated underneath with 1″ poly sheeting cut to fit snugly and filled any remaining gaps with spray foam insulation. This should give us better road noise isolation than the ultra shitty job the spray foam guys did at the factory.

On top of the insulation we laid 3/4″ marine plywood and took a note from GMC and glued it down with 3M 2 part panel bonding adhesive and screwed it in with STAINLESS screws. Another theme here: Replace with better than factory.