Ok, I used the Inland Marine Sealant. Washed the floor down beforehand with soapy water - a few slow leaks showed up, cracked material - the usual. Unscrewed the fill valve and took it out, poured the whole quart bottle into the floor, reassembled the valve, and put some air in but not too firm - just like instructions said. Then, yeah, I rolled and flipped and turned that sucker good - sometimes faster, sometimes slower. One of the bad spots is where the tubes meets the flange, all around the perimeter - cracking - slow leaks, so I rolled the floor slowly around on perimeter. and every other way. Did all of this for around one half hour, then a little every half hour, again just like instructions. 4 hours later pumped it up firm. Two days later it's holding well. It just might be functional and get me a few more years out of this old raft. So, right now, I say it worked.
The raft tubes don't leak at all. I'll do the spring cleaning, glue down whatever needs it and reassemble with frame. Fished the upper Madison one week ago out of a drift boat and it was fantastic - 16" to 20" rainbows galore. Gonna try that again in the raft and maybe the Big Hole in a few weeks before runoff starts in earnest.