Personally I thought the Overhaulin' team's approach was a bit OTT on the floor, I just didn't get that part. If you wanted to stiffen up the structure surely you'd look at the side sills which is what Lotus did with the S1 elise, which incidentally also has a very thin (1mm ? 2mm ?) aluminium floor albeit with stiffening ribs.
If you think about it you don't put a lot of weight on to the floor and the seat spreads your weight over the attachment points which rarely (if ever ?) fail. Whilst it looks a questionable design under modern eyes I think we need to put it into perspective; they built nigh on 10,000 of the things and while I accept something could punch through the floor, it's not a common occurrence, is it ?
The whole car is lightweight and if you look hard at the side sills or doors then you see 3mm GRP. The front & rear wings, roof, windscreen pillars, in fact most of the car is thin GRP and side impact protection is a few years away with these cars. Added lightness or skimping on the resin ? It's Lotus.... you decide
Brian