Floatation Suggestion:
Big foam "noodles" into the hulls. They weigh almost nothing and will support a lot of weight. They're also good for stuffing into the mast and beams.
Sol Cats:
I bought my yellow Sol 18 in New Orleans in '77. Sold it in Houston in 1983. Never had a problem with it. It was a great boat. I miss those old durable, solid boats.