The old, apparently discontinued Sevylor Trailboat was always too small and fragile. The other vinyl boats that could be bought for under $50 worked better, but were very fragile and needed tender care. But the fist hiking traverse of the Alaska Range (Tok to Lake Clark) in 1996 by Kevin Armstrong, Doug Woody and others was made with vinyl rafts. They floated the Nenana and the Stony Rivers among others with expedition-ish loads, too.
Many people completed Wilderness Classics in vinyl rafts including Dick Grifith in 1982, and others throughout the 80's and 90's.
Back in the 90's when only vinyl rafts and the wee Curtis Design boats and used Sherpa Rafts were all that was available, Barney Griffith (he made the first kayak descent of Devils Canyon of the Susitna, Talkeetna Canyon, and Canyon Creek in the 70's) often packrafted with his dad Dick in the Wilderness Classic. Barney told me that a good paddle was more important than the boat. When pressed for what he meant by "good", he said stiff so that you had control and could keep the vinyl boat or fragile little Curtis Design off sticks and rocks and out of holes.
Below is a video from Australia of people running Class II and III in inexpensive vinyl rafts. By the way, "lilo" is Aussie for air mattress.