Yes it is colder in manitoba, I bet it rather bitter at this very moment.
I used 1/16" sheet.
Yes the center rib is structural, but also to help secure and line up the cells.
Yes, the cells will have to be strapped to the box. That part hasn't been made yet.
The sealer will be ProForm PF224 Urethane sealer, an automotive windshield adhesive will also work well. Any real autoparts store will carry something like that (i.e. other than crappy tire)
The reinforcing on the box lid was done with a roller machine, so nothing was wielded on. It did warp it a little, but it doesn't matter because it will be bolted down and forced into the correct shape.
I don't know if ventilation is required. The unit cells have a vent port on the top center of them, but they arent supposed to "gas up" unless something is wrong. Flooded Lead acid batteries have a water based electrolyte, so production of Hydrogen
and oxy is a fact of life with them even when all is well. One of many reasons why they loose efficiency under higher load.
There will be enough room for forced ventelation if I decided to add that later. For now, i am not convinced that its required though.
The front part of the box is not large enough to fit any batteries, so I'm hoping the charger will fit in there. If not, it will work as a junction box to tie the two rear battery banks together and then send power to the front of the car. I'm sure I'll find a use for that space.
I'm thinking the battieries might require cooling in the hotter summer months, so thats why I won't put any insulation from the start and allow the aluminum box to transfer the heat out unimpeded by insulation.