Thank you, Bogertophis and Gio. While external appearance may not be fully indicative of health, it's probably the best we can go off of, along with making sure the prey items offered aren't excessively fatty. I agree that Gus Rentfro is a trustworthy source of guidance, and I myself have used Vin Russo's book as a guideline for shifting my boa feeding schedule into a more seasonal pattern.
The exercise component makes sense too. I have basking shelves and perch rods for them to climb in their enclosures (and it is amusing to watch how they negotiate the perch rods in a way that is very different from truly arboreal snakes like GTPs). However, I wonder what else would strike a good balance of providing them more opportunities for physical activity without causing them too much excess stress.