I really wanted a Packa/Parcho for hiking the Pacific Crest Trail in the rain, but I wasn't willing to spend the money or sew one myself.
For rain I used an umbrella and rain chaps and some plastic bags. I liked the rain chaps a lot. The plastic bags didn't work very well because they got sweaty.
I really like hiking with an umbrella. It's so sensible. Doesn't work too well in overgrown, head-high wet brush, however.
I went over 7 days straight with wet feet in brushy Washington. My shoes and socks disintegrated. They only time I had dry feet was when I slept, but it turns out that if your feet are dry overnight, you won't have foot problems.
I used a big garbage bag for a pack cover. It worked great. It would puff out and make a lot of noise so I had to get creative with how I stuffed it behind my back. I don't think anything sold would work better than my trashbag. I cut little slits for my shoulder straps so the bag covered the entire pack. I stuffed the open edges into the back pad pockets and the thing was completely watertight. I wanted to keep my pack dry because it would get very heavy when wet.
I ended up buying a vinyl rain poncho in Snoqualmie Pass at the Chevron because of the inability to stay dry in wet, overgrown brush with just an umbrella and rain chaps. Naturally it stopped raining as soon as I started carrying it. I had it all rigged up with an elastic waist band that would wrap the back under my pack and leave the front free for ventilation. A poor-man's Packa/Parcho.
I don't think you need to worry about your pack while you are setting up your tent. You can usually find a sheltered spot under trees to set up your tent. It can often be surprisingly dry under a tree. Dry enough to set out your pack and get dinner cooking while you set up your tent.