Most Featherbed tanks sit on rubber tank mounts on the frame and a tank strap that go along the top of the tank to hole it on, on my Wideline frame my tank sits on the rubber mounts and is not bolted down at all, my rear seat is mounted to the top rear shocks the same as the Commandos, I use a Commando Interstates seat ( solo seat with the hump) but had to change the mounts to fit in the right position for the Featherbed, the seat sit right up to the rear of the tank, in over 38 year with this set up I have had no problems at all.
The reason I don't clamp or bolt my tank down is when I first convered my 850 to the Featherbed back in the early 80s is I had a major fuel fire and what saved my bike was I was able to pull my tank off and away from the fire, the fire was caused by a leaking fuel tap and running volictity stacks without air filters the bike backed fired through the carbies when kicking it I was on the bike when it went up, never ran volictity stacks ever since, lession learned the hard way, but my tank still sit on the frame without being bolted down.
Ashley