After players’ feedbacks, we found that a « hang back and tech up » strategy could be played. This runs counter the « game spirit ».
We decided to add the rule below (last step of the Camp phase). This solves the problem.
When you set up your Camp, if your Scout is on the last space of the route (5 steps downriver from Saint Louis), then get rid of all the resources and all the Indians (to the Pow Wow area) that are on your boats. Discard all the Encountered Character cards you may have recruited since the beginning of the game.
However get back the starting character cards you may have discarded.