I asked around a little bit about this, it sounds like the best option is just to pick the shortest route you can get as distance traveled doesn't seem to significantly affect the number of seals you get. I only did imperial trading for a very very short period of time and my training level was very low but I was getting a seal about every other run. A higher level trader I spoke with said they got about 1 on average per run (occasionally 2) and that it took them about 3 hours to get 10 seals. You might want to ask around a bit more and see if you can find anyone with a bit more experience, since a lot of what I know (and the people I've talked with) is speculated based on only a short period trying out imperial trading. I don't know of anyone that stuck with it.