The T-50 staples I had used to tack the aluminum flashing to the bottom of the subfloor were not holding very well. This is likely because the recommendation to use T-50 staples is based on the assumption that one is going to be using a trailer with preinstalled wood decking which will effectively hold the flashing in place. However, my trailer is fully metal and has no such supports. I opted to addtionally affix the flashing with 7/8" plastic-cap, ring-shanked roofing nails. I'm now satisfied that the flashing will stay in place.