I just found this board and would like to address your questions about Double Eagle sleapers.
I have driven two KW W900's with custom sleepers, so I know a little about the subject.
The air ride units are not isolated from the cab and there is no boot. They remove the air ride sub-structure from the cabb Then build and install a new sub-structure to run the length of the cab plus the new sleeper. The new sleeper is mounted to the sub-structure and attached to the cab by a small(less than 2 inches) boot to accomidate minor flex.
This set-up rides like a dream.
As to the question on price, it's all in how you look at it. The second custom sleeper I had, an ICT Sundowner 132", cost $51,000. It was speced with a shower, toilette, full size, double door fridge, two burner range, double stainless kitchen sink, 30 gallon fresh water supply, 20 gallon waste water holding, RV type dinnette, full size bed, 12kW generator with sepperate heat and air units for the sleeper.
Being able to cook my meals in the truck, I was able to save close to $150 a week in food alone. Over the course of the two years I drove that truck, that amounted to $15,600.
Idle time was reduced from 45%, in my previous unit, to under 3% for a fuel savings of over $5,300.
At the time of sale, figuring for normal depreciation of the power unit, we made back 92% of the initial cost of the sleeper.
Food savings plus fuel savings plus 92% ROI equals $67,820 in my pocket after the sale. Roughly $16,000 profit after I lived in it for two years.
Keep in mind, when calculating value, that these sleepers are designed to travel 100K plus(double that amount for a team operation) miles every year they are in service and provide a comfortable living environment while doing it.