Termidor is the best product for termite treatments, hands down. It is odorless, and not only that, but it is made to bond to the soil and it will not run off or leach through the soil, so it is perfect for treatments in wet conditions. on a crawl space house, you would trench and treat around the exterior of the structure, and you also need to trench and treat around the piers under the crawl space. As long as you are using Termidor, you are not required to treat the inside perimeter or inside the hollow block, but of course if you want to you can.
You can do that if you choose, but it is not as effective as drilling the slab inside the garage. This is because the garage is a separately poured slab, meaning the termites could come from deep underground and come up to the surface under the garage slab, and enter the wall where your door is going into the house untouched. You don't have to drill every wall in the garage, just the walls that are not exterior walls, where you have living space on the other side of the garage wall and apply Termidor. So it is a personal choice, but drilling the garage walls is the best way to protect all entry points.