Another thing about slide in/out ramps. I have never seen a set that wasn't bent all to heck after a few years. Plus it seems no matter where the slot is for them, it is unhandy.
In all the years growing up around the flat bed business (Dad always owned an OTR truck, even when he himself worked a "real" job) I never saw a pair of ramps. Like the other poster said, they get loaded at docks, by forklifts, cranes, even helicopters. But I never saw a truck pull up and the driver snatch a set of 12' long ramps out from under the trailer to drive something up on it.
Once again, I really stress the 10k pound axles if you are looking at a 30' trailer. The temptation will always be there to "fill it up" and two 7k axles will be overloaded very quickly.