UWDave,
I saw you said you didn't have access to copper in your area. Having a copper backing bar makes sheet metal welding EASY. All of your welds will look like they were professionally done by a tig welder with decades under his belt if you use one. Hell, I have one in particular that's almost 20 pounds and 1" thick I use for high amp welding. My normal one is around 1/4" thick. Do you have a torch (oxy/ace, oxy/propane)?
In a pinch, you can get copper pipe, hammer it flat, and go to town. You can also braze a coating over a piece of steel and make a spatula heat sink. Both help immensely. It's a literal night and day difference. Spot welding / filling holes with 100% penetration, without any lack of fusion, and without a 1/4" blob hanging out both ends takes 3 seconds to do, with your eyes closed. It also makes welding gaps on sheet metal child's play. Just weld directly to the copper in the gap, then wash the puddle over the sheet.
Call up a metal recycler in your area. That's where I've bought my copper blocks/scrap from. I think I paid around $4.50 a pound. It's worth 10 times that to a welder, and probably twice that if you do sheet metal work!!
Otherwise, looks amazing!