Hardware & Soft-Ware

Mod: Insulated Floor – Part Seven

The final part of the floor installation entails fastening to the vehicle’s floor and caulking the edges to reduce moisture penetration.

Project Insulated Floor Content

Tie Downs & Wheel Wells
Paper Plywood Templates
Floor Insulation
Fasten Insulation With Glue
Spray Foam Application
Plywood Installation
Hardware & Soft-Ware

What You’ll Learn:

  • How to drill into your cargo floor.
  • How to inlay a T-nut.
  • How to install & shorten your bolts.
  • Where to apply undercoating.
  • Where to apply caulking.

What You’ll Use:

  • Drill.
  • Drill Bits.
  • Forstner Drill Bit.
  • Wrench, Extensions & Socket.
  • Hacksaw Blade or Oscillating Multi-Tool.
  • Caulkgun.
  • Hammer.
  • Tape Measure.
  • Small Brush.
  • Wheel Chocks.
  • Safety Goggles.
  • Sandpaper.
  • Optional:
    • Tarp.

What You’ll Need:

  • 10 Stainless Steel 1/4”-20 x 1” Serrated Flange Bolts with a Full Thread.
  • 10 Stainless Steel 1/4”-20 x 1-1/4” Serrated Flange Bolts with a Full Thread.
  • 18 Stainless Steel 1/4″-20 T-Nuts.
  • Undercoating.
  • Locktite PL-S40 Caulk.


Approximate Duration For This Project: 4-1/2 hr.


Each vehicle is different and the materials I used are for my 2016 Ford Transit MR LWB.

The plywood floor has to be secured to the vehicle, as it also functions as a base for all the cabinets and appliances in the van. In case of an accident, you have to make sure that everything stays in its place.

I used two techniques to increase the hold of the floor. The first is using rabbets/dadoes along some of the plywood edges, where each sheet adds holding power over the other sheet, to create one solid sheet. The other is T-nuts and bolts.

elevator-boltOriginally, I wanted to use ‘fanged’ elevator bolts, but they stick out at the bottom and may make the installation of water tanks more complicated. Therefore, I choose to use 18 T-nuts and bolts; about six for each plywood sheet. Certain locations were blocked by the fuel tank and I ended up using two less, but I feel assured that they will do their job. The dadoes on each plywood sheet enhance that.
The hardware is all stainless steel to minimize rust and is bought with different length bolts. I try to install then within the floor ribs, where the distance to the plywood is minimal, but was forced at some locations to place them outside the floor ribs. That added approx. half an inch to the length of the bolt.
I did not anticipate that the T-nuts would lie on top of the plywood, so I used a Forstner bit to create a shallow hole in the top of the plywood as wide as the width of the T-nut. That was done after the hole was drilled from below and before the hole was widened at the top ¼ inch to facilitate the T-nut.

With the T-nut solidly attached in the hole and to the plywood, it is easy to insert the bolt from the bottom. Afterwards, cut all bolts off with a hacksaw or oscillating tool and sand flush.
Stainless steel hardware can be quite expensive and you may save some by ordering on-line.

To add extra protection, use some undercoating to cover the bolt locations. Let it dry and give it a second coat. Shake the spray bottle well, before each use!

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To minimize moisture penetration, I use a caulk to fill the ¼ inch gap between the plywood and the walls. I used Loctite PL-S40 polyurethane window, door & siding sealant, as the polyurethane may have a less corrosive impact on the steel than other caulks.

This is the final part in this series of articles about the installation of an insulated sub-floor. At a later stage the entrance area at the sliding door will be finished, when the finish flooring is installed. At that time, the finish flooring will also be extended a bit into the rear of the cabin. At the rear doors, a wooden threshold is planned at a later stage, that covers the plywood dado; it will extend a bit above the plywood, to account for flooring material.

Plywood Floor Installation

Gather all the tools and materials before proceeding. Regularly fit the materials, to avoid costly mistakes.

  • You’ll be working under and around the vehicle; use wheel chocks as an extra safety measure.
  • Remove the spare tire to allow full access under the vehicle.
  • Measure the distance between the edge of the plywood at the rear doors and the bumper as a point of reference.
  • Under the vehicle, locate the specific floor rib for the hole.
  • Measure back from the bumper to get the exact location.
  • Drill through the floor and plywood.
  • Use goggles to prevent metal flakes from getting into your eyes.
  • Inside the vehicle, drill a shallow hole with a Forstner bit.
  • Widen the original hole for the T-nut to fit.
  • Hammer the T-nut flush to the plywood.
  • Install the bolt from the bottom up.
  • Repeat this 17 more times.
  • The shorter one inch bolts may just fit, but many have to be cut flush with a hacksaw.
  • Use coarse sandpaper to remove any sharp edges.
  • The plywood may not be flat, but the bolts will pull them down and lock them in.
  • Optionally, you can spray undercoating over the exposed bolts. I do it twice.
  • Finally, fill the gaps around the plywood with caulk.

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Stainless Steel Hardware

I decided to go with all stainless steel hardware. The serrated flange bolts are inserted from the bottom up and grab the metal floor. The T-nuts are mounted flush to the plywood. I was unsure about the length of the bolts and ordered both 1 and 1-1/4 inch lengths. Some could be installed without modifying, most had to be cut down.

Ordering this stainless steel hardware on-line can save you some money, even in smaller quantities.

  • Stainless Steel 18-8
  • 18 T-Nuts 1/4” – 20 #10484.
  • 10 Full Threaded Serrated Flange Bolts 1/4” – 20 x 1” #17452.
  • 8 Full Threaded Serrated Flange Bolts 1/4” – 20 x 1-1/4” #17453.

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Quite a bit of work and sometimes difficult to find the locations under the vehicle to drill the holes. Ultimately, a feasible job for anyone who can hold a hammer and use a drill.

The bolts and nuts used during this part of the project, were acquired on-line and the cost was about $25.00. The undercoating and caulk was acquired locally. Total cost $34.20.

Other projects of this Van Conversion:

I’m just a DIY’er with a lot of common sense, but with some of the projects, I use some tools and materials, that require you to really know, what you’re doing. Always read the manual and consult an expert if you’re in doubt.

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  1. I looked back through but I couldn’t find what thickness of plywood you used; was it pressure-treated?

    1. It wasn’t pressure treated (these tend to be less flat and less ‘healthy’, but a good option). I did treat it with a poly-urethane and used overlapping joints for stability and to prevent moisture.
      I decided to apply some insulation between the floor ribs and a 1/2 inch ply on top (and another 1/4-1/2 inch flooring on top of that at a later stage). My reasoning was, that with a medium high van and me at 5′-8″, I had to minimize the thickness of the floor, so I can stand up straight in my van. If you’re substantially shorter or if you have a high roof van, I would apply an extra layer of Poly-Iso under the plywood for better insulation.

      Van Williams

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