WARNING!!
BEFORE YOU START THIS PORTION OF YOUR BUILD! Please read my post here about a factory born issue with ALL (to my knowledge) Sprinter Vans.  

Now that we've got that out of the way, there are MANY different opinions on the Internet and forums on the best way to noise deaden (if any) and insulate a van. This is just what I went with after researching a lot of the different options. I would highly recommend reading through the forums and other blogs to see other peoples setups, because my method may or may not be the best way to do things for your own personal build. That being said, here are the deets of my setup:

Products Used:
Sound Deadening 1 & 2
Insulation: 3m Thinsulate sm600l (~50 linear ft. for a 170 Sprinter)
Spray Adhesive
 

Tools Required:
Ruler/Measuring Tape
Heavy Duty Scissors
Sharpie
Painters Tape (Optional)
A Friend - For Roof and Bigger Panel Installs
 

Skill Required:
3/10 -  Measuring and Cutting is just time consuming.

Time:
I spread this out over multiple days/weeks.

WARNING #2! Before you insulate, read this!

SOUND DEADENING:
Since this part isn't the most physically challenging step of the build, I mainly wanted to use this post to provide information on my thought process in choosing how I went about choosing the products I used for my own purposes. This may get lengthy, so be prepared.

Man this was a stressful decision to make for me, it's hard to even pick a place to start, so let's just jump into sound deadening.

I scoured the Internet for weeks weighing and comparing cost vs. "how much will it really help" vs. how much do I need? It's pretty clear that Dynamat is the top dog in the sound deadening category, but boy is it expensive! When looking at outfitting an entire van (~90 sq. feet) it wasn't reasonable to be spending around $15/sq. foot. That would put you at almost $1400 just for sound deadening, which is outrageous!

That gets us into "how much do I really need", which really boils down to your own personal preference and how much road noise you can deal with. Those who are outfitting cars for some serious audio systems will tell you to cover every inch of the trunk, door, floor etc. so you get a solid "thud" when the door shuts or the bass hits. Personally I didn't want a rattling car, but I'm not too terribly picky and figure there is going to be sooo many other things that are going to be making noise in the van, that I ended up deciding to go a take a mid-ground on how much I would be applying. 

This got me into looking towards Dynamat substitutes, and while I did mention you should ALWAYS do your own research, I'll give you the Cliff Notes (is there a trademark on that? Do I have to put the TM?) version of my research. FatMat seems to be a good second quality-wise to Dynamat, so I ended up going with FatMat MegaMat. This is because the MegaMat model is the only one of FatMats products that is 100% (so they say) Butyl. This is important because the other options are a combination of butyl and asphalt, and asphalt is bad because it needs to be heated up to stick, and can fall when it gets above 100 degrees outside. 

HERE is a great comparison between different models that helped me make the decision.

So all that being said, I got about 25 sq. ft. of MegaMat and applied small strips of it to the larger more flimsy panels in the van that were susceptible to rattling due to lack of strength. Note, there was a bit of sound deadening already in some sections of my panels, so I worked around these. The goal was to get enough material in the panel to strengthen it, but not to cover the entire section. That seemed unnecessary. That all being said, I did run out of MegaMat slightly before I was all finished, and ended up getting a bit of Dynamat that a friend had leftover from their build. To me, the Dynamat did feel a bit stiffer, but audibly I could not distinguish a difference.

Personally, I was able to hear a slight difference in sound when knocking on the panels with MegaMat vs. those without any, but my girlfriend couldn't tell. I would assume that you would hear the biggest difference when measuring exact acoustic road noise in an empty van vs. a fully sound deadened van (which people have done!) but I did not take the time to do so. *Queue the photos* 

WARNING #3! Before you insulate, read this!

INSULATION:
Insulation is an important piece of both keeping hot air inside the car during the winter, but also keeping hot air outside of the car during the summer. Some of you may have plans to camp in the snow and some of you may have plans to stay in the warmer climates with your travels. Either way you'll need some kind of padding between you and the elements aside from the very thin sheet metal walls of the Sprinter.

I plan to be camping for multiple days in the snow during the winter, as well as out in the desert during the summer so I needed something flexible as well as capable of not molding in the case that some water did get into it.

There are many different types of insulations you can go for; thinsulate, wool, denim, spray foam, rigid foam, fiberglass, reflectix, low-e, the list goes on. You can also combine a couple of these together for added protection, here is a good summary of each type that may be helpful when deciding on what you prefer based on necessity and cost, but I highly recommend doing your own research on the different materials to determine what will work best for your own application. 

For my own needs, I chose to go with a combo of 3m Thinsulate and Reflectix. The reason being that I wanted something fairly easy to install and something non-permanent, I did not want to put spray foam insulation in because this seems fairly impossible to remove if in any case I would want to. I also got deep into researching what was "best" and came to the conclusion that there is no "one best answer" to this question. This is one of the most heavily debated topic I've seen on the forums and everyone has their own reasons for going with one material or the other. In the end I ultimately got a little frustrated with how long I was spending on research and decision making and realized there likely isn't a DRASTIC difference between materials when you consider all the other factors (wood paneling, cabinets, etc) of what will be in the van, so I just settled on going with the Thinsulate because a couple of my buddies had put this in their vans and it seemed like a solid and common choice.

*Disclaimer - If you plan on installing rear windows, it is a good idea to do so BEFORE installing insulation.*

I did also throw a layer of Reflectix over the top to try and repel heat a little more in the summer because those grey metal walls love to radiate the hot air into the car, but that being said I did wait to do this until I had run all of my wiring to their proper locations while I still had access to the panels beneath.  

After the insulation was in I ran all the electrical wiring (entirely different story and about 6 months of time on this build) and then put Reflectix over the top to sit between the insulation and the wood paneling that I planned to put over the top which you can read about in my post about Wall Paneling and Decorative Covering.