Step 1: Find a Used Dolly on Craigslist With Inflatable Tires.
Step 2: Go to Home Depot With $24.99. Find a Cooler in Your Garage.
You will also need a cooler but I assume you have one in the garage already (you won't be drilling any holes or damaging it in any way).
*lay your scrap lumber, already cut to 48" in length, lengthwise on the dolly's runners
*place the cooler you plan to use on top of the lumber, at the bottom of the dolly closest to/over the wheels (this will likely be the heaviest part of your loaded rig once it's filled with ice, salt, and beverages)
*place the mixing tub behind the cooler, centered on the dolly and flush/snug with the cooler (it MUST be snug to hold the cooler in place without the need for straps or similar)
*mark the location of where your tub needs to be attached (to keep it snug with your cooler) with masking tape or similar on both the TUB BOTTOM, the LUMBER, and the DOLLY FRAME (I used painter's tape)
*drill holes (2 for each U-bolt) through both the lumber and tub (measure twice - drill once - not all U-bolts are identical spacing)
*bolt the entire assembly together like a lumber sandwich: DOLLY + LUMBER + TUB (place washers inside the tub... plastic will become brittle after wear and tear in the sun and salt)
*the handle is simply a short length of FLEXIBLE PVC piping bent like a horseshoe with the gap closed by elbows and a straight length of pipe, glued shut with heavy duty PVC cement, and, then lashed onto the dolly frame/handle with heavy duty zip-ties doubled wrapped