The two biggest challenges I see with a gas oven in a skoolie are heat and humidity. In order to burn gas inside the oven cavity there has to be fresh oxygen going in and hot combustion gases coming out. Those gases are coming into the bus. When it's already hot in the summer, that makes the interior even hotter. Those gases are not only hot, they're also full of water vapor. That vapor can make the heat even more unpleasant in the summer, it takes extra effort to condense out if you're using air conditioning, and it can make condensation problems in cooler weather.
Two years ago I bought an over-the-range convection microwave oven for my home kitchen. We use it for baking at least once a week, not to mention the dozens of times a day it gets used in microwave mode. The kitchen also has a relatively nice full-size 30 inch electric convection oven. We use that only for things that are too large to bake in the convection microwave (turkey, more than 2 baking sheets or casserole pans at a time, etc). That happens about five times a year.
We liked the convection microwave so much I bought another of the same model to put in the bus. Unfortunately our interior finish is yet a long way off, so that unit is still in the box and I can't report any experience with it on the road.
The comment about "cottage food laws" and possible income suggest that you may really need a full-size oven. Maybe more than one? It might be worth considering whether gas or electricity will be the best fuel for baking in the tiny space a bus provides. An electric oven is fully sealed and insulated, so minimizes the heat and humidity problems I mentioned about gas ovens.