Is there any reason not to bury aluminum triplex cable in a rigid
nonmetallic conduit? This is out in the country, where I don't care
about finer points of the electric code, but it needs to be safe and
generally in compliance.

I ran #6 triplex "Periwinkle" cable from my parents' house out to the
tool shed a few years ago. It's a 120/240V 40A feeder, and the shed has
its own service equipment and grounding electrode. The wires keep
getting knocked down by falling branches. Last time was during Ike, and
they were running two generators instead of one because of it and almost
ran out of gasoline. I'm fixin' to visit them for a few days and was
thinking about rerunning the feeder underground. Wha'd'ya think? The
ground is sandy and real easy to dig.

(It's also a Federal Pacific panel, and I'd like an excuse to replace it
with a Square-D or GE or Siemens. My dad doesn't really wanna replace
it, but it's a hazard and I'd be happy to pay the ~$50 for a new panel
and breakers.)

Thanks,
Bob