Way to go with the trailer.
My wife and I are in the process of taking this route since we both have PA's. We were putting one on top of a fullsize truck and one in the bed with the bed extender. We are both in our 20's and in pretty good shape.
One of the examples you gave with slick footing and damp conditions happened to us a couple weeks ago. We were at a boat ramp, and it had rained for several days it was just dark. We were loading up and I have had my wife hold the rear of the PA about chest high and I take the front over the top of the truck on the Yakima bars, and then I go to the rear and continue to push upward. We have a fiberglass tannau cover on the truck so there is no way to stand in the bed. Well the weight of the kayak on the lower end (her side) forced her to slip backward she held her ground, but it really scared her. So we decided not to go back out until the trailer is completed. I want to get this thing done. UPS and the trailer company have screwed us it should have been completed a week ago and now I'm missing some great fishing.