Maui Shtang

As for the floors you have to do what you have to do some times, most would frown on this approach but you aren't building it to resell so only you will really know. You will have to make sure it is completely sealed though top and bottom and I would use a good undercoating as well, any moisture or sand can and will seep into the smallest cracks and cause worse rust than you replaced. The automotive industry has been bonding more and more parts to cars instead of welding for over a decade now with no issues what so ever, do a google search for "bonding instead of welding" and you will find all kinds of info, process and technique.

Good luck!

Pak