I have a 220V miller spot welder, it performs flawlessly and I have buzzed together a bunch of Minis and MGs over the years. I can't speak the the harbour freight ones, but if they do work, I recommend one as a tool, spot welders are HUGE time savers

I purchased a HF gasless, flux welder a few years ago. $190.00 Runs off household 110 current. While I'm no expert, I have done a fair amount of welding thru the years. This unit requires patience. It isn't going to heat as fast as a better heavier model. It will do a very good job if your prep work is top notch, and you don'tmind doing a bit more cleaning up when your done doing your burn.

With that said, I was very confident when I completed my inner and outter sill replacement project.

I used the 220 volt Harbor Freight welder last year on my 1966 Mini.  It worked very well.  You just need to clean the tips.  I have a 220 volt HF welder that I picked up for $850.  It is better than my Miller 175.  It is fantastic.

Dogscarf

Another option is to get a spot weld nozzle for a MIG welder. They actually work pretty well. I've used mine a few times with good results.

https://www.eastwood.com/mig-spot-weld-kit.html?utm_source=youtube&utm_medium=annotation&utm_campaign=2012-03-08&utm_content=MIG%20spot%20weld%20kit

Over the years I have considered buying one of the HF spot welders but I haven't because I never thought I'd use it enough to justify the cost.  I considered buying a used one but people seem to think "used" means "I get all my money back and more".  Seriously.  Looking at Craigslist, Offer Up, and others you'll find people selling used HF spot welders for $180 or more when brand new HF sells them for $160.  It used to be that used car parts and tools were priced at about 1/2 the cost of new. 

I also looked at (and experimented with) the DIY spot welders you'll find documented on YouTube.  When I tried my DIY version all I got was smoking welding cables from the transformer to the tongs.  I guess I'll stick with plug welding where I can get away with it.

I used one on Dolly (Dooders' Countryman) while rebuilding it.  Don't know if it was a 120V or 240V version (probably 240V), but it worked fine with no problems at all.  Being cheap and analogue there is obviously an element of user ability involved...

Don't overwork it, practice on plenty of scrap pieces first.

The 120 volt one does an okay job if you don't try to push it. Just make sure you properly prep the metal, and keep it to two layers. It doesn't have enough grunt to burn through paint. If you're doing more than two layers at a time, like the sills or valance, you might want to go for the 240 volt one, or just do plug welds. Also, the tips that come with it are about what you would expect for cheap Chinese junk. The jaws have an odd thread size, but with a little work they can be re-threaded to work with better Miller tips.

I have used one. Does pretty good. Heavy as hell. Get the 240 volt. When you need tips get a better brand of tip.

Yeah and that's what I was planning on doing with my panels is plug welds. That spot welder just seemed like it could be a good buy if others have used it with success

The following is hearsay, not my personal first-hand experience.

Over the years a number of members of this board have posted their opinion on the HF spot welders.  Most say that the welders do work on the exposed seams.  The consensus seemed to be that the 240V model worked better than the 120V one.

Having said that, many people do not make true spot welds when fitting the new panels.  Instead it is common to punch holes in the outer panel and plug weld thru the hole to the inner panel.  

Wondering if anyone has used it on the sills or valance and wondering your experience. It's pretty cheap and looks like it will work good.