Gary, I'd just buy one. They're well made and work perfectly as a foot rest. Plus four has the 12" version unless you have a narrow body. Yes its just two fixings through the ply floor although there are two holes that I presume are for through bulkhead fixing. I didn't bother as I didn't want to drill that and I didn't think it needed any more security although I did use some rather large stainless repair washers underneath.
