Building a canoe trailer doesn't have to be very complicated.

Get a jet ski trailer that holds 2 Jet skis.  Remove the winches.  Now your canoe will rest on the bunks like the jet skis did.  Load the heavy gear in both canoes.  Make a rack to support the other two and attach it to the center of the trailer.  Load the remaining gear in the other canoes.

If you need additional room for gear, weld metal mesh on the floor of the trailer.  Load the gear and bungee cord it down.

You can find one of there trailers, used, at any marine dealer.

This set up works well and really doen't require much modification.