I'm about to attempt what your describing (foam under aluminum deck) within the week. My current plan is foam the sides, and leave the middle open for water to head towards the back. And I'm going to lay in plastic sheet first, so if I ever need to fix anything under the deck, I won't have that foam stuck to everything. I'll have pictures up in my thread when I get it done.
Your making the right decision working in aluminum. Not really more expensive than wood + epoxy + carpet + weight + maintenance. MIG will work fine, just not as slick looking as TIG. Biggest problem with MIG will be the distance from the welding machine to all areas in the boat combined with needing to keep the feed line as straight as possible, as the aluminum wire will often not feed well if the line has sharp turn or loop in it.
Your making the right decision working in aluminum. Not really more expensive than wood + epoxy + carpet + weight + maintenance. MIG will work fine, just not as slick looking as TIG. Biggest problem with MIG will be the distance from the welding machine to all areas in the boat combined with needing to keep the feed line as straight as possible, as the aluminum wire will often not feed well if the line has sharp turn or loop in it.