from what ive gathered, one or two generations of inbreeding are fine, but then you should do outcrossing.

something like an inbreeding coefficient can be calculated, and with the right ways of outcrossing that number can be reset to zero. When parent A and parent B have completely different ancestors, the offspring will be back down to an inbreeding coefficient of zero, even if both parent snakes on their own do have an inbreeding coefficient. Many reputable breeders make use of that "reset button" and regularly do outcrossing to keep up the genetic health, and this gets easier to do with a bigger collection.

a calculator for inbreeding coefficients i found, it also lists which ancestor contributed how much of the genetics:
http://www.czerwonytrop.com/inb/index.php?full (its designed for dogs, but the math is exactly the same, works just as good for snakes).

if you keep doing it for multiple generations, the first thing that will happen is that fertility rates go down. but one or two generations is generally accepted, and often done, especially in recessive or double recessive projects.