My recent purchase of a 2002 Express 1500 didn't come with any manual (Chevy or Starcraft). It only has 2 DC plugs up front. I'd like to put 2 more in for the middle and back seats. There is a fuse panel behind the driver's seat with 4 fuses and no labels, which seems potentially promising.

Anyone know if there's a sane/clean way to add extra outlets?

 

Digital manuals (PDF) are available from the GM owner's center.
https://my.gm.com/home

I assume you're talking about the cigarette lighter style 12V power sockets.
Run a fused wire from your battery to wherever you need. If you have an upfitter stud in your underhood fuseblock you could use that too.

The fuse block behind the seat you speak of doesn't sound factory. You could try scouring the internet or contacting the various Starcraft support companies out there. Otherwise you might be out of luck with that one.

 

I'd run directly from the battery or a existing smaller terminal the connects to the batter if there is one. From there I'd run fused wires to each location.

If you are going to use these for USB power primarily, I've added these to my older vehicles and they work great. This one comes with an inline fuse but I use a 4 way blade fuse block under the hood instead for easier access.

 

Neato, I've added one of those to my sport bike right behind the triple tree before. Worked great.

 

I'll second on the USB jack. A lot of them offer more current (amps) than the standard cig adapters. And that could mean faster charging.