This project has evolved over the last few years. I wanted a cart to carry all of my surf fishing gear and beach paraphernalia. I had seen other people with such carts, however, they seemed to be for solo operators whereas I always had my kids gear to tote to the beach as well. I just needed something bigger and cheaper as well.
Today's cart is also a trailer for pulling behind my beach bike, as shown in the photo, however, there is a handle for pulling by hand indicated later in this Instructable.
Link to bike project: http://www.instructables.com/id/EXTREME-FAT-TIRE-BICYCLE/
Step 1: Basic Frame
The basic frame is constructed of 1 1/2" X 1 1/2" aluminum angle. That's what I had laying around.
I figured what the overall dimensions I needed for my large cooler, tackle box and a large bucket for the basic frame rectangle.
The corners were clamped tightly, then drilled and screwed. This seems to be adequate for the connection after several years.
I added a length of angle across the frame near where the axle would go, for added stiffness.