Two years ago at the Arlington Air Show in (of all places) Arlington,
Washington I parked our bus next to a stretch bus.  It was definitely a home
job with the following mods:

Middle stretch of course.  The bus was made from two buses (a red one and a
white one)with overlapping middle sections (if you stand next to a bus you
can see vertical seams that go from top to bottom at the front and rear of
the slider door.  This bus had the two sliders still in place but one of
them was bolted shut.

Chevy V8 (small block) with what had to be a Toronado transaxle.  The
radiator was sitting on the roof sticking straight up.

Camper stuff.  All a hack job with a big stove and refer.  Sun faded
sculptured pile carpeting of various colors finished the look.

Not pretty but damn did it have room inside...

Also a few months before I got a modem I saw two Eurovans that were stretch
jobs. Both were identical white and looked like they were panel vans that
had black anodized aluminum frame slider windows.  The middle sections were
about 50 percent longer than a regular one with no torch work evident.  They
seemed to be pretty plain inside like they were meant for utility duty.

When I first saw them I was driving down I-5 and they were on a flat bed
truck, fresh off a boat it looked like (plastic wrap, grease pencil, etc).
A month later I saw one driving in my local grocery store parking lot with
some people that looked to be of middle eastern origin.  

While I have been known to hallucinate, I am quite sure of what I saw.  It
is definitely longer by quite a ways.