If the foam is sealed as a sandwich construction between the outer layer and the inner floor, water won't condense there. Water condenses if warm moist air hits something cold. If the foam is trapped in the sandwich the warm moist air won't be in contact with the foam and therefore can't make condensation. In the case where there is no insulation, the warm moist air from the inside (all that heavy breathing, or just breathing either way) hits the cold floor where it causes condensation. This is also eliminated by putting the foam on the inside as the warm moist air hits the non-cold foam and then doesn't condense. One other way to get condensation as Madjack eluded to is to Have A/C on the inside of the tear, little or no insulation on the floor and warm moist air on the outside. In that case water could accumulate on the bottom of the trailer. However, that too could be eliminated if the insulation is fully stuffed as to prevent warm moist air from coming in contact with the cold trailer bottom, or just sealed as a sandwich
So, there are a couple of ways of solving the problem, but they all involve keeping the warm moist air from hitting something cold. I you do put it in the inside it should cover the ENTIRE floor -- no gaps around the perimeter.