I ride rollers out in what is effectively a garage. That's a huge help over the winter. I also go to the gym and do weights, mostly high-rep, and a spin class. Some intervals once a week over the winter are a huge help. The big deal when touring is of course climbing hills, and intervals are the way to get better at that, also actually riding hills when weather permits. The more hills, the better. You'll want to get comfortable on your touring bike with a load of course and get comfortable paring that load down much below what you want to take, as opposed to what you need to take. But IME training with the load is unimportant as long as you are riding a lot of hills. Whatever increases your enjoyment of hill riding is the thing to do.