I ended up with a 2001 Toyota Sienna. It doesn’t have stow and go, but I want to be able to take the seats with me in case I need them. I was just going to jump headlong into making a bed platform that fits over the top of the back seats with their backs folded down and see how it went, but then I thought I should see if anyone else has tried it and has any advice first. All the videos I’ve seen have the seats being removed or folded into the floor.
This may or may not work out well, it all depends on how low the seats fold down to, and the height of your mattress. If it’s too tall it may be uncomfortable or impossible. The only other down side is it will give you less storage room.
Another option is to replace your original seats with ones that fold down into a bed. I believe that was an option that year, so you may be able to find some in a wrecking yard. Some years had whole camping packages available, with an attached tent, folding picnic table, and portable kitchen, along with a powered fridge between the front seats.
If you’re handy and ambitious, you could replace the original seats with DIY ones which would fold into a bed and provide additional storage as well, or even build it into something similar to the VW Eurovan campers. If you really wanted to go crazy, you could even add a similar pop top. A friend did just that using a donor roof from a wrecking yard, and with the top down, you couldn’t even tell it had a pop top. Totally stealthy in cities, but standing room and an extra bed when outside of town camping. VW made Lagun style tables very popular as well.
A middle seat can be added as well.