I needed a way to take my TI off of the trailer easily to do rigging on the boat or work on the trailer without the boat on it. My trailer does not allow for the amas to be deployed because it has an upper level that is supported by uprights placed just outside the amas when folded.
I used a pair of Harbor Freight Dollies and built 2"x4" risers to match their dimensions and attached them with a couple of 1/4"-20 T nuts and bolts. The 3" grid that spans the dollies and provides an attachment surface for the 1 1/2" pvc conduit bunks was just some material I had on hand. I would have used lumber to span the riser/dolly pair otherwise. The bunks are just held to the grid with velcro cable ties and the grid is held to the dolly /riser pair with 1/4"-20 T nuts and bolts through some pieces of bar channel that clamp the grid down to the 2"x 4" risers. The whole thing disassembles easily and the doly/riser assemblies do double duty as saw horses to work on other things in my shop. The pvc bunks work so well that I can pull the boat off of the ones on the trailer and onto the ones on the cart with one hand. I put a wheel chock behind one of the dollies to keep the cart from moving.