Big progress today! Several friends and family members came over to visit with the new grandbaby, and one of these friends was J., a cabinet maker who has given me good advice several times and helped assemble the trailer frame, back in April. I asked him about how to lift up the trailer in order to tuck the canvas edges underneath. I suggested that 2 people could lift one end of the trailer up with pry bars, while a third one slid a 2x4 across from one side to the other, then the trailer could be lowered down onto the 2x4. The other end could be lifted the same way.
J. said it would be easier than that. He crawled under the trailer and lifted up one end of it WITH HIS ARMS!

My daughter and I slid the 2x4s in place. Then he lifted the other end, and we blocked it. I went on to glue all the canvas edges in place, then J. got under the trailer again and we removed the 2x4s while he held it up! Talk about your incredible Hulk!
He said it wasn't as heavy as he expected.
Here are some shots of the finished edges. I used a lot of push pins along the bottom and around the wheel well, and we put shims in some places where the canvas wasn't snug enough with the frame (just till the glue dries). J. complimented my work, saying that when he lifted it, the frame was rock solid with no flex at all. He says that he is now considering using canvas when he builds his tear next summer!
In one of these pics you can see the small folding counter I installed yesterday.