Yeah, I hear you all about the sturdy wood, and the homo depot cart.
Here's my thoughts
1 the garden cart is pretty heavy ( i have one), plus I can disassemble this one and throw it in the raft if needed. Saves having to come back to the put-in.
2 The additional wood is overkill, plus I can use the plywood as a bench seat. Again- saves having to come back to the put in. Plus with just the boat and frame it's not an issue.
The OP was looking for a solo cart to bring boat from car to river, I had the wheeleze for my sea kayaks and the plywood bench for my 14'. Turns out I spent $0 on this and it worked - Optimal performance- maybe/maybe not. Did it save me having to haul the 130lbs of boat down to the water twice last weekend - You Betcha!
I'm sure there will be other "modifications" but that's why we boat right? Continually improving the line.....