way to get around population size for cabbage

Cabbage seed tends to be expensive, so I'd like to grow my own. However, maintaining a population of cabbages is time and space consuming since they need to overwinter and a large population is required for genetic health.

What if I bought two open pollenated varieties and selected one strong plant of each for overwintering? They would then cross in the spring and I would harvest and plant the F1 seeds, but not continue to grow them out. Instead, every few years I'd retrieve my original package of seeds from the freezer and grow out another couple of plants. That way, the two packages of seed would last almost indefinitely.