A few problems with this one:
1/ The holes cut into the floor will need to be throughly watertight otherwise they will rust straight through
2/ Unless the holes are immediately next to a chassis member, the floor will tear as it becomes tightend-up
3/ You would need a secure plastic/rubber gasket between floor & securing strap otherwise the webbing will fray
4/ Too near a hot exhaust pipe will melt/set alight the webbing
5/ Floors and chassis rails are designed to flex, therefore your webbing straps will need constant re-tightening as they expand & contract with temperature chance/body flex