I have that hand truck. Its excellent to use however the tires don't hold air between my infrequent uses of it. If the air loss isn't in the tread area I doubt Slime in the tires would help. (HF seems to sell a lot of Slime, I wonder why?

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I've thought about welding up a frame I can mount on that hand truck to make it a trailer for towing my harvest ladders down into the orchard. If I'm not towing the 4x8 trailer then I carry the 8 and 11 ft ladders crosswise above the front loader and zig-zag around dodging tree props. Towing these and longer ladders behind me lengthwise would would work better. Another project for when I get around to it. Has anyone done this?