It rains a bit where I live...here's my method;

Take pack off and prop on feet - take out small tarp and lay on soaking ground - lay pack on tarp - fold tarp over pack to protect camera bag from rain - set up tripod - put focusing cloth on tripod then a small rain poncho over cloth - put 4x5 under cloth, attach to tripod, and open camera - tie strings on camera's carrying handle through holes in focusing cloth - (I cut my cloth into a triangular shape with the 'top' of the triangle chopped off so the cloths lens board ends reach below the focusing knobs - I did this so I can move around under the cloth and it won't slide off the camera in the rain) - then the lens goes on - then the small rain poncho's neck gets snapped around the lens so that it overhangs the lens slightly - then it's business as usual despite monsoon rains or four foot snowfalls in a day.

Murray