Hi D'Arcy,
Early this summer, I ran a 44' Gozzard from Annapolis to Cleveland with the rig on deck, and that trip featured some pretty sloppy conditions both on Delaware Bay, and Lake Erie...
The supports had been massively overbuilt by Southbound Rigging at Port Annapolis, but in my observation it was the use of the ratcheting straps that contributed the most to keeping the whole arrangement secure. The stability of the sort of simple A-frame you describe is inherent, but the addition of fore & aft "spring lines" - and the ability to keep them bar-tight with racheting straps - is really what made the biggest difference, and kept that rig from budging so much an an inch...
best regards,
Jon