Jim, Now having gotten under my 390, I believe the driven fasteners were used. Take a look at the attached and let me know if you agree. If so, I suspect I'll cut out a section of the Coloplast and not attempt to remove an entire section. Thx again.
Well, they did not spin out like a screw but they did loosen up enough to pull out with a little down pressure on the washer while turning. A few required a hard pull with vice-grips but they all came out with out too much trouble.@MartySchwartz - great to hear you got those nails out and replaced them with TEK screws when you buttoned the underbelly back up.
I was able to spin those driven nails with a small impact socket but they would not spin out for me. So I gave them the beating they deserved
Glad you had an easier time removing yours