My penny's worth.
A P-30 chassis is a P-30 chassis except for the day it ran down the line.
Mondays and Fridays were always days to avoid but you have no hope of
knowing that information.
There are three styles of Airstream motorhomes. There's the "classic" style
with the aluminum skin all around including the rear cap. The Excella is of
this variety. There is the fiberglass version with the "shark nose". Both
were built on P-30 chassis (the P is for parcel). Small busses, delivery
trucks, etc. are built on this chassis. Expect a medium truck ride because
it is a medium truck. The third variety is the "flat nose" with fiberglass
body. These were built on a Freightliner Custom Chassis so they had
generally had Caterpillar 3126 engines. They went by various names including
Clipper, Cutter, and Land Yacht XC (the Freightliner XC chassis).
Interior workmanship - I've seen and owned better - we currently have an
Airstream Land Yacht XC. It doesn't compare to the Royale or the Holiday
Rambler we've owned.
Windows - in the classic variety aren't made for cold weather - plexiglass
in a frame.
Insulation - I don't know about "in the day" that the Excella was built but
now they are using a brown variety of the pink, spun stuff. It has a better
R factor than the spray foam that shrank like GMC had.
Service - They treat you nicely at Airstream factory and dealerships -
that's about as far as it goes.
The house - as pointed out, a camper/RV is made of off-the-shelf stuff. Fans
from here, appliances from there, wiring from down the road, toilet from the
plumber, etc. The furniture is the only thing customized for the unit. At
least they didn't use fiberboard but real plywood. I hate fiberboard with
plastic laminate.
Airstream - it's a cult just like the GMC-TZE crowd. People are people
wherever you go. The Airstream forum has lots of good folks just like here.
Comparison - there will be more space in the longer Airstream (if it is
longer) but there will be leaks somewhere, more than likely.
The 454 - back when it was in the truck it wasn't designed to last as long
as we drive things today. Again, it depends on when the engine was
assembled, what the guys were watching for, and whether they cared.
Otherwise, parts is parts and quality is like oats - there's the kind before
it goes in the horse and the kind that comes out of the horse.
Design - other than the Airstream look with aluminum skin, there is no great
attempt at engineering like there is with the TZE's chassis. If you are
concerned about driving/riding - get the GMC.
Byron Songer
Louisville, KY