Since the oak is veneered, you will want to minimize the exposure to weather unless it's exterior ply, which I doubt. Even though it's varnished, moisture may/will find it's way under the plys and will eventually ruin your nice job.
Actually, teak planking is not that expensive if you buy anywhere other than WM or other than finished boards. An internet search will yield rough cut lumber that while comparatively pricey, isn't that bad. Find a friend, local wood shop, or school with a wood shop can mill it and you'll save a lot. If you can, find plantation teak because it's a sustainable resource.
Another trick that we use when running the A/C is to take a large beach towel, fold it in half, and hang it over the companionway hatch like a thick curtain. I lay 6" of towel on the top of the hatch under a hatchboard to keep it in place. Keeps the A/C in place and makes entry/exit easy.
Sabre 38 "Victoria"