painting inside the trunk

Dave, if POR15 is put on as you described, ie, wire brush the surface rust and paint it on, then it seems to last well in low or no traffic areas such as the trunk or interior floor boards. However, I've seen a lot of vehicles where the POR 15 was in wheel wells or on the bottom of the car, and if one little breach occurs in the POR 15 surface, then you have a major problem with rust forming under the POR 15 layer. As with any other product of this type, you have people who swear by it and those who swear at it. :)