There is an inexpensive "spot weld cutter" tool that is basically a 3/8 inch hole saw, usually used to remove spot welds during classic car restorations. I used these to cut out over 150 spot welds on a Mercury Cougar. Works great on auto steel, should breeze thru aluminum.
Available thru most...
Remember to acount for an attached outboard in figuring storage building depth. That said, I would go with the 14 ft trailer....dealer photos shows that the trailer''s bow support is not welded, but on a clamp style base...can be easily loosened and moved forwad up the tone to accommodate a 15...
Manufacturer specs for the Grizzly 1448 is a 17.5" transom, which would take a short shaft.
If you are still getting the runaround/no call back from the dealer, you may want to call Tracker customer support (417) 873-4555, or 873-4555. They will likely put pressure on the dealer to get things...