The floor is by far one of the things I am excited I figured out and hope my problem solving ways will help you too. It is a shame I didn't make a video sooner so you could see how it was all put together, but am hoping the photos will help you out.
The first thing you'll notice in the mini van is how the bottom takes a weird dip at the front. This is not an issue in converting a cargo van, but is always going to be an issue when converting a mini van that is not designed to be a camper at all.
Two big things I took into consideration when doing my floor. First it needed to be insulated and second it needed to be completely bolted down. The last thing I wanted in the event of an accident was anything to happen to Baron (my dog) that could have been prevented. I could only imagine the wood floor falling down if the van were to roll.
Lucky for us the floor has the bolts that you would normally clip the seats into and those are going no where. I took advantage of it and ran pieces of wood up them and bolts through those clips. I did this both vertical to the side and horizontal from side to side near the front. Your can see them in the photo sticking out.
With the dip at the front I added the row underneath to help level it out. I threw as much insulation as I could in between the pieces of wood and then took a full piece across the top once everything was levelled out. This also helped to cover the tops of the bolts
Next I added a full layer of plywood. I used a 1/2 sanded pine, but depends how much room you have. Remember for every little bit of thickness is that little bit of head room you lose.
Once I put that piece down I screwed it right into the pieces of wood I have bolted into the seat clips. At this point venting is secure.
*** A little trick that might help ... the pieces of foam you used to run across the level floor. Take those out and use them as a tracing guides to cut the plywood. It is far easier than attempting to measure weird angles. This way they will fit perfectly on top of one another. ***
Once you have the plywood screwed in place it is time for the wood flooring. That is the easy bit. A good old nail gun and I did glue down the first row as well. It looks so nice when it is completed.