Touche - my Luegone Velocity XT has a pre-welded steel floor 
The posibilities are endless. They have got a klicky that takes them to our klicky .............................................................
that makes me soooo happy
Pah!
To be fair Mike, steel or ally, a rock at speed will rip through either with great effectiveness.
Far more pertinent point is to run decent underfloor ground clearance!!!
If you are worried about puncturing your floor, use kevlar.
I highly recommend running a tube under your seat. Remember that your butt is held down by the seatbelts attached to the frame. If the floor is
pushed up by a rock/curb/timber etc you are going to get everything in you pelvic area crushed. Two thin pieces of sheet are not enough to stop
anything solid. A diagonal cross tube will certainly help.
Cheers.
Just wear cycling shorts under your trousers. If it's going to get you it will but if something is sticking up that far it's going to hit
somewhere else before it gets me as the car is lower at the front and it will lift the car if it hits a chassis member. A friend of mine had an Escort
XR3i when they were new and ran over a silencer that fell off a lorry in front of him It ripped the bottom of the car after it had demolished the
gearbox and the car was written off, only 2 months old.
It may suprise you how often cars get banged up in that area.
What I often see from customers who have done some accidental offroading over curbs/medians is an impact near the front of car (crossmember area)
then another good dent near the rear of the rear floorpan on a sedan. Right where a Locosters ass is 
. I assume the car bounces up from first
impact, then comes down on the rear. I have seen dents about 2" deep on the rear in 16/18ga steel. I will sit a lot happier knowing that I have
a steel tube under my ass..... especially the way I drive
Cheers.
[EDIT] oh ya, maybe you just solved what I was going to do for seat padding. I have lots of downhill cycling pants that come with padded undershorts
[Edited on 9/5/06 by C10CoryM]
I've been considering an X or V brace in each of the floor sections, to reduce the risk of lozenging if I hit anything offset. This sounds like
another justification for doing that.
One of the Aussie V8 Supercars ran over a drainage grate at Shanghai last year and ripped open the floor the length of the cabin (at 250kmh )
the same happened to montoya in the malysia grand prix last year iirc, he was lucky that it was the sidepod not the centre bit because it punctured through all the layers of carbon fibre.