6” mattress works with the back seats just folded down. No need to buy additional support like crates or table leg platforms to put underneath. Just move the seats back against it. I’ve slept on both sides of the mattress as one is firm and the other soft. I prefer the firm side as I’m a back sleeper, but tend to sleep on my side after hard hikes and use the softer side on those nights. Always wake up rested and pain-free.It does take up the ENTIRE trunk when folded and back seats are up. Kind of a bummer so I’m contemplating buying a black mattress bag used for moving to cover it when not in use and leaving the back seats down all the time and the mattress extended. If you plan to haul other gear AND have 3+ passengers then you will have to huck this thing up onto a roof rack or basket or put it into some form of trailer hitch basket/system.Knowing what I know now having slept on this mattress, I think the 4” version would’ve been acceptable. I got the 6” as I was worried over time the 4” would lose too much support and figured 2 extra inches could/should compensate. The quality feels like it’ll last longer than my current car camping fetish.Although the cover that comes on the mattress is rated to be “Washable & Waterproof”, I still bought a mattress protector from SafeRest to go over it all. This way all the body oil and muck will be on the fitted bedsheet put over the sheet protector. I can take both or just the bedsheet off for easier cleaning. Removing the W&W cover seems like it’d be a pain to put back on. I’d rather not mess with it.Lastly, I’d strongly suggest getting the “Carry Case for Milliard Tri-Fold Mattress” that matches whatever size bed you bought. As the mattress cover has no handles, the case makes it much easier to move around. Definitely recommended for storage outside of your vehicle.Based on reviews for most of the floor beds on this site, I was terrified to get a piece of chemical smelling garbage, but this doesn't smell at all, and it very comfortable. It is firm, but I prefer this. It's very warm as well.Totally changed my car camping comfort level. Fits my XL cot, a twin bedframe, or just sleeping on the floor for grandkids. Love it.I ordered this mattress to replace the horrible back breaker that came in our new camper. The first mattress that was shipped arrived quickly but was the wrong size and style. I initiated a return on Amazon (unable to find a way to contact Seller). I had to repack and take the mattress to UPS to ship it back and then re-order the mattress again. Unfortunately the price had gone up since my first purchase and since there wasn't an option to exchange, I had to pay more for their shipping mistake.This time the correct size/style arrived. Again, fast shipping. This mattress is supposed to have a firm and soft side so you can flip it to your preference. I generally like a firm mattress but even the soft side is quite firm, however a great improvement from what we had. The mattress and cover are a good quality. But, if you don't like firm, this isn't the mattress for you and you might want to check out some of Milliard's other styles.This thing is huge and we love it, movies in the living room with the family will be awesome. We are a family of 6 and we all fit perfectly on this king sized mattress!Received this last night and it is comfortable. Expanded nice pretty quickly. Measures as promised. Photos were taken about 16 hours after receiving it.Comfortable Good value.I keep it in the back of my suburban. Super comfy.Love how firm and comfortable the mattress is. Quality material. Very happy with the product.Très confortableIt is perfect. Extremely comfortable.The quality is excellent. Very comfy also.