Sounds about right to me. I used to part own a 1973 Sundowner and we always kept a load of useful stuff in the back - tow bar, oil, cleaning materials - that kind of thing. As we pretty much knew the weight of it, it could be included in the W&B calcs. If you don't have that kind of thing, work out how much weight would be needed to put you nicely into the envelope, and then get something that heavy - a few bricks perhaps, or a small plastic barrel that you can fill the required amount with water.
It was a beautiful aircraft to fly, having learnt on the PA38/PA-28 type aircraft. One day I did a quick walk around, then went flying. I found that I ran out of backward trim, and had quite a hard time slowing the thing down. As soon as I realised that I had forgotten to check that the heavy stuff was in the back, I managed to adjust my flying style to suit, and landed as soon as I could - deciding that I would not use flaps so that I would be landing quicker, with more wind over the stabilator. All in all, not a nice experience - but since then, I have never skimped on an initial walk round.