I wouldn't recommend it.  Find an old popup and REbuild it as you would
like.  I have seen many of these done that have come out great.

QD Steve asked:

I would ask this question in three other places in order to get better
response:
<http://www.arveeclub.com> (despite the name, dedicated to pop-ups for
the time being)
<http://www.popupexplorer.com>
<http://www.popupportal.com>

The reason I suggest asking there is that I have seen the kind of sites
you are looking for.  Someone would have links.  In addition, there are
lots of people with sites about modifications to their pop-up, some of
which might be useful to you.

My own approach would be to find a pop-up that is being sold as
"chassis only" or "utility trailer only" and start with that.  If you
can get a roof and lift system, great.  But pop-ups didn't always have
roofs, and so a 100% tent roof could also work, eliminating the need
for a lift system.

Austin

Greetings,

I've given some thought to a project similar to yours over the years and
have come to a personal opinion/conclusion that a pop-up is one of the most
difficult types of camping trailers to construct.  There are issues with
specialty lift systems, bed extension systems and supports, and making it
all weather-tight.  Not to mention the expense of custom canvas and what
would undoubtedly be a lot of custom fabrication.

You could take the advice offered here and find an old(er) pop-up and
rebuild it yourself, but an even easier project would be to purchase an old
enclosed trailer (like an old U-Haul) and convert it to a camper - at least
that would eliminate the problems with lift systems, bed extensions, etc.
One conversion that I came up with many years ago involved an old U-Haul
enclosed trailer that had sections of the side walls cut out that would fold
out and be supported from underneath for single beds on either side of the
camper.  The canvas system for the bunks is pretty basic, and the cutting
and reinforcing for the walls-turned-bunks when folded down is fairly simple
and easy to make weather-tight with overlapping edges and gaskets.  The bunk
supports are simple pipes held in place in square U-brakets and pins to
prevent them from dropping the bunks when loaded.

As for the rest of the interior it's just a matter of making cabinets and
seating, plumbing and electrical.  You can even mount an A/C unit on top if
you want to spend the $$$.

Just my two cents worth.

Cheers - Jonathan