I would assume that Brossard Manor has a road leading to it and that this road runs through an open field. This is because sentence elements that are close together are supposed to relate to each other, and manors have roads leading to them.
But, aside from your query, this sentence has a misplaced modifier, as "the area" cannot be "using BattleTech to resolve this situation." I would have edited this sentence like this: "Under BattleTech rules, a dense forest surrounds Brossard Manor, which connects to a road running through an open field away from the manor." Or, if I wanted to be wordy, I could edit the sentence like this: "Under BattleTech rules, there are four things: a manor, a dense forest, an open field, and a road. The manor is in the dense forest. The dense forest is next to the open field, and the road connects to the manor by going through both the open field and the dense forest."