I wouldn't worry about the rubber washers - NVH (noise, vibration and harshness) isn't exactly a Sammio strong suit.
After all, the real fun with these cars is feeling that you're part of the machine, hearing, feeling and smelling all the components doing their stuff. Totally the opposite of a modern car where you're completely detached from the action, even at 155mph.
Btw, how're you planning to fit your floors? On the Spyder the frame sandwiches the floor between it and the chassis, then you 'glass the inside of the body to the floor to give it strength.
Just a thought...