hmmm..tricky problem.
im not all familiar with desert environments, (never even been to one!
but IMO all you can do is grow the plants "normally" and see how they do..
get DEEP trays of water..
I have been using "the tray method" for 16 years..never had a problem.
I have never even heard of this "rhizome melt" that Pyro mentioned..not saying it doesnt happen,
(and if it does, I doubt its because of too much water) but I wouldnt worry about it..
sarrs generally cant be over-watered! some people keep the water table nearly at the surface for extended periods..
from what I have seen, the tray method is "tried and true" and works great..
you want LOTS of water, especially in your environment..dont worry about it being too much water!
"too much" is always better than "too little" for Sarrs and VFT's..get trays like this:
Keep the tray filled all the time, to the top, so that maybe only 2" to 5" of the pot (depending on the pot size) is "above water"..
you could try to rig a sunshade to filter the mid-day sun..maybe some slats or shade cloth that shade the plants between 11:00 and 2:00 or so..mid-day when the sun and heat are the most intense, but then allows "full sun" in the morning and later afternoon..
IMO, Zone 6 is too cold to overwinter sarrs and VFTs outdoors in pots..
Zone 6 is "borderline safe" if plants are in the ground, in a bog, with heavy mulching..
but definately not safe for plants in pots..
you need to be Zone 7 or higher to have no worries for outdoor dormancy..
but it sounds like you get cool enough in the fall that the fridge might work fine for you..
I have some thoughts on zones and fridges here:
http://gold.mylargescale.com/scottychaos/CP/page2.html
Scot