Awesome boat, Country Dave!
On the subject of TIG welding, I'm an AWS certified welder with about 2 decades experience. So, I'll add to the conversation, a few things I've learned over the years.
Thoriated tungsten is for steel and stainless, it should not be used on aluminum because it contaminates the weld. It might be easier to weld with thoriated, but it's not recommended for aluminum.
A foot pedal is DEFINITELY a big help, especially for starting out. Once you've done it for a while, you can learn to weld with fixed amperage, controlling the puddle by using a larger diameter tungsten and filler rod, and varying arc length, but it's still tricky.
When welding aluminum, metal cleanliness is of utmost importance, ESPECIALLY with TIG. Use only a stainless wire brush, and only use this brush for aluminum, nothing else! Aluminum oxide interferes with proper puddle formation, and this oxide forms immediately upon exposure to the air. It is this oxide which makes aluminum nice and shiny, but it is also this oxide that is problematic. It's really a SOB with anodized aluminum, such as T-tops, because that's what the anodizing is, an oxidizing process. That said, you'll want to use plenty of elbow grease and wire brush the weld area until it turns dull-looking, then you know you have removed the oxides, and this includes making sure to get the edges of cut material, as well. Make sure you brush not only the weld side of the material, but the back side as well, because of the possibility of oxide pick-up as the metal begins to heat.
Make sure your filler rod is clean, as well, or it will just melt into a blob, and won't wick into the puddle when you dip it. Stainless steel wool is probably the best way to clean the filler rod before use, because it removes the oxide. DO NOT use sandpaper, it contains aluminum oxide, which is what we want to get rid of! And do not use regular steel wool, or this will cause iron contamination. If you don't have SS wool, a scotch brite pad is the next best thing. But if nothing else, take a clean paper towel and wipe it down to remove excess dust, etc.
For TIG welding aluminum, the rule of thumb is 1 amp for every .001" of material thickness. Welding mild or stainless steel doesn't require as much heat for a given thickness, and this is because aluminum has 3 times the thermal conductivity of steel. When welding steel, the heat is localized, and can be concentrated onto the area, rapidly creating a puddle, even on thick material with low amperage. But on aluminum, the heat instantly spreads out, so, it requires more amperage. Also, pre-heating with a torch will help on thick pieces.
However, unless you have a big industrial TIG machine, you will find a point at which you can't turn it up enough to weld aluminum, and this is generally around 3/16" (or 180-200 amps) for most buzzbox welders using a hi-freq unit. Also remember that when using a hi-freq on AC, you must de-rate the machine's duty cycle by 1/2. So, for a 20% duty cycle machine at full amperage, using hi-freq, you only have a 10% duty cycle before you start tripping breakers or burning up your machine.
Due to those limitations, once you get above 3/16", you really need to use MIG to weld aluminum. For thin material TIG is champ, but on heavier stuff, MIG is the way to go. However, if you want to guarantee a liquid-tight weld the first time, such as welding aluminum fuel tanks, then TIG is what you want. MIG often has porosity inclusions that would otherwise be non-critical, but on something like a fuel tank, any inclusion is unacceptable, and a place for a leak to begin, so, things like this are usually done with TIG.
