Thanks for the comments guys. I have a lot of hard work into this trailer, trying to figure stuff out, even after having built probably 50 trailers in the past. I hope the info helps someone.
I know one thing, the 2.5" crossmembers flex a bit....not much, but its there. They are 16" o/c. I'm going to weld a piece of 2" angle to every second one, turning the angle into a 'C' channel, just to stiffen them. The skid steer puts a lot of weight right close to the center of the trailer. I'm just paranoid tho....
I got the screws from our hardware supplier, SIRR Fastner in Thunder Bay, Ontario. The are expensive, but being self drilling/tapping, and with the big flat head, they are the best to use for wood decks. They are galvanized too, so no rust.