i got my trailer in may, 2000. i started using the turnbuckle system right away. i got the idea from a trailer that i looked at before i bought mine. your friend must not be tightening them down enough. i don't have any damage to my floor other than the paint marks from the stands (i use painted steel stands). i have a turnbuckle set-up on each side of my trailer. if i bring a third bike, i use tie downs and put the bike in the center-front.
i think i will put in some of that e-track. it looks handy. i always have a bunch of gear (generator, cots, stove, lawn chairs, etc.) tied down all over the place. the e-track would make that much simpler.