: So to do double duty, I am considering taking a poncho for
: rain gear and also using it for a skirt while I have it on, in rough or
: rainy weather.

Go for a decent spray skirt and decent rain gear separately. I'm not sure how you expect a poncho to serve as a sprayskirt. It will either be huge and baggy -- catching rain in folds, or it will be open on the sides, allowing waves to splash in.

You can make a lightweight sprayskirt from nylon cloth, and a poncho too if you wish. Nylon fabric from the fabric store is about 2 to 3 ounces in weight for a yard. Your total weight for a poncho should be under 12 ounces, and a sprayskirt would be under 6 ounces. Campmor and several other camping supply places sell a liquid urethane product for recoating tents and sealing seams. You can roll this onto your home-made poncho and sprayskirt and let it dry.
Campmor also sells fabrics. They used to have a urethane-coated nylon fabric that could be used for tent flies. You could cut your raingear from this material and then just need to touch up the seams for complete waterproofing.

Making a comfortable harness for portaging your boat is probably more important than saving a few ounces of weight. You need to be able to see where you are going, and to keep your balance. The smoothly finished kayaks are slippery to grip when wet, and handles at the bow and stern are nearly useless for a one-man portage. If your gear weighs too much you just make two trips, or move half your gear 50 to 100 feet, and go back for the second half. If you make your haul in a series of short stages you need never let your gear get out of eyesight. It is slower, as you cover the same ground twice, and you need to unpack and divide your gear, then repack on the far side -- but you can portage as much weight as you can pack in the boat.

Consider a packframe, and also consider how you will get it into your hatches. Hmm, sounds like something I should design.

PGJ