I posted some pic's of the cradle here somewhere but I can't find them, and I quess I didn't save them, but here is a couple I do have. The mainframe is kiln dried 4X4 held together with 4" angle iron welded at a true 90 degree's, and two 1/2 bolts at the ends of each 4X4, one bolt vertical and one horizontal, bonded with Loc-Tite premium polyurethane glue board to board and to the angle iron. the 1X4 on top of the side 4X4's has holes in it where the bolt heads and washers
stick up on top od the 4X4, the 1X4 is also screwed and glued to the 4X4, and there is a 2X2 on the inside of the up-rite 2X8 that is screwed and glued to both the 1X4 and the 2X8 with 3 1/2" screws to hold the 2X8 up-rite, it's pretty strong. The swivel wheels are "knobbies" that make it really difficult for them to turn, and they are a little light weight for the whole boat, load rating @ 300 lbs each, but thats all I could find.