I'd vote for fall myself. How about late September to early October as a start date? Since these pieces are pretty big, maybe an extra month might not be a bad idea for completion. The Trumpeter guns are supposed to have huge numbers of pieces.
The St. Chamond kit is supposed to be a bit of a mess. I hope not! If the kit is unusable, I'll be very pissed (it was expensive), and may just build the Trumpeter Morser plus rail transport.