Here is my beach trailer. I ride it to the beach, the drag it across the soft sand, and tow it on the firm sand to where I want to set up.

An old Schwinn kid trailer, stripped, with wood floor.

The first iteration was nearly impossible to drag on deep, soft sand with the 20 x 1.75 tires.

I replaced the tires with 20 x 4 1/4" rear tires from a Schwinn OCC Sting Ray. I just forced the large tires onto the small rims. Used the original small tubes, there was no way I could get the fat tubes in there. I don't think the tubes are doing much, just a little bit of support for the tire bead, at best. I had one tire in my parts pile, and had to buy a 2nd one. I lost quite a bit of width squeezing those tires onto the narrow rims.

Much better with the new tires. Only bogs down in the ruts left by Jeeps and pickups.

The floor is thin pallet wood. The sides are incomplete, still using the kid trailer sides. I made the sides removable, attached with pins, instead of bolted in in, for quick disassembly.