John, this subject has been discussed on here in the past but not to the greatest of detail and it's probably time to advance the record. Many have only used the lighter duty household or HVAC foil coated bubble wrap which can be found at some home improvement stores or here on the web. It's really kind of a weak product but I guess it suits those needing to pinch their pennies.
There are a couple of different types of insulation I would personally recommend. Depending on what areas you would like to insulate and what you would like to accomplish. You can insulate these babies better than factory if you choose.
The product Sean (NewellCrazy) just posted is a great product and yes it is used by Newell Coach along with the products I am describing below. There are some people that have preferred not to opt for this improvement while repairing their coaches. I strongly disagree with those decisions. Go for the Gold when working on your luxury coach and not skimp. It will payback in energy savings and sound comforts.
The Newell factory has done a great job compared to most other manufacturers out in the RV world. But, if you so choose you can take things a step further. I myself have done so on other coaches, autos and boats over the years and many of those products are still being used today.
I do not like or recommend the foam board for use on overhead areas in any moving vehicle unless in is encased somehow like maybe a basement door shell, but then again that will still most likely leave nooks and cranny's left unprotected. I would go with a closed cell spray foam insulation under your basement ceiling, it is a two part foam you can apply. In fact the manufacturer and bottler are not too far from me, but they only sell directly to private label manufactures or distributors. I'll provide you with some links for that product below.
The engine and generator compartments are another story and there are commercial grade aircraft and yacht engine room insulation that I have found to be the best. Here is a link to a new thread covering the engine compartment installation.
http://www.luxurycoachlifestyle.com/...dproofing.html. You will find diagrams and examples at this link. We will update things as we have additional information to share.
This post will be updated as I dig up my information and photo's. Please be patient with me and standby. thx