The best time seems to be late Spring through mid-Summer. Weather is very important - a late Spring snow might not be as much fun as a sparkling clear weekend. After that it's hotter and dryer.
If you can find out when there's a fly0in there, try to avoid it. Especially the 180/185 fly-in, as it'll be very crowded and pretty noisy.
Most people generally get fuel at McCall. Coming from the east, Challis might do. For me, the important thing to do is make sure that you can definitely get out to more fuel. I come from Colorado, and try to tank up at McCall or Challis on the way in, and watch my fuel while I"m out playing. McCall is about 20 minutes from Johnson Creek for me in my Cessna 180, so it's not a big deal.
I've found that in the early morning, the humidity from the creek causes dew and a fogged windshield. These clear up after the sun's up from behind the mountain. It's way worse if you're tied down on the east side of the runway and better on the west side.
The effect was fun to figure out. There's a mountain on the east and west sides of the runway, and the runway side, the east side, of the west mountain warms up first from the sun. The air flow is down the east mountain, across the creek, past the planes, and up the west mountain.
For day trips, there are a number of fun places to fly to, and McCall is one of them. All the back country airports are fun and many are challenging, so do your homework and go in the morning. The nearby town, Yellow Pine, is worth a visit, and there are plenty of hiking opportunities right from the field.
An excellent reference is "Fly Idaho," by Hanselman, at
www.flyidaho.com. It's a must-have. The state of Idaho also publishes an airport directory which is quite good but doesn't have the things-to-do and history that Fly Idaho has. The state has a good map showing a number of airfields that are not on the sectionals. You can get those here:
http://itd.idaho.gov/aero/Facility Directory/index.htm.
Camping is good there. You can camp by the plane or in the campground 100 feet away. There are showers and toilets and might even be cut firewood. Don't expect to sleep late because people will be up very early running up and taking off.
Land to the south and take off to the north. Make straight-in and straight-out approaches and departures unless you're utterly familiar with the plane and have lots of back-country experience. And call your position, altitude and intentions often.
McCall's grass runway will be mowed and is usually decent. Some of the other airports might not be. On my C-180, I have the small 600-6 tires and no wheel pants and don't have a problem. The plane grosses at 2,550. I can't say what to expect from wheel pants, but some time ago at one of the other fields out there, I met two guys in RVs. One had an RV-4 and the other had an RV-6, and I think their wheel pants were on. They did well. I was impressed.
Dave