I've been working at Harbor Freight part time for fun.
I can tell you a few things. The company is horribly run, from the top down. Their is no training, no accountability. They are more concerned about opening more stores than they are about stocking, staffing and training. What you ran into shouldn't have happened, but it's not a big shock to me either. It's also very possible/almost certain that neither of them were trained to operate the forklift.
They try to run stores on as little labor as possible, they hire just about anyone. The store I work at has multiple felons and at least one guy I'm fairly certain is homeless. The managers aren't micromanagers like they need to be with that level of worker. Low wages, no standards, no training, no oversight, it makes for a horrible customer experience.
Mark my words, Harbor Freight will be sold off in no more than 5 years. They are pumping the company to build as many stores as possible with no regard to actually being able to operate the stores. They are going to dump the business on some investment company, who hopefully will have experience is running retail and will build out the infrastructure and make the business actually run smoothy. Right now the upper management is about on par with what you'd find at a buy here, pay here used car dealership. They could do a lot better with no more effort, they'd just rather be crooked and not give a damn. (The original owner sued his son for taking over the company and pillaging it. The son has a f'ing gulfstream V, tens-hundreds of millions in art, a 65 million dollar home in Bel Air, plus another beach front Malibu mansion a half hour away and likes to make big political contributions)
Calling the store manager may or may not do anything. Calling to district manager will probably get you better results.
Take the offensive with the district manager, don't be a jerk. But just simply state:
You drove from an hour away because this is the closest store.
You were willing to buy a tool box, full price - no coupon. (I don't care if that's true or not, if you really want to go over the top, tell them you were interested in a replacement plan for the box too)
The store was not staffed properly and the ones there were not willing to go above and beyond to pick up the slack
They have a surplus of the items, but they are not even easily accessible for the employees
Why is their stock room so packed with stuff that they can't reach one of multiple huge items?
You were willing to spend 10 times what the average customer spends in the store, and they talked you out of it
Getting them to give you 20% off the box shouldn't be too difficult. Getting them to ship you one and them to pick up freight is possible, but is likely more work than the DM will want to do. If the DM is willing to go above and beyond, 20% off and free shipping to your door might be possiblity.