I spent a week in Wyoming with my mom visiting Yellowstone and the Grand Tetons. Before I left, I ordered a 25'x10' Firestone EPDM Pond Liner from bestnest.com. They had the cheapest price and free shipping for $165. The box was delivered while I was away, so the day I got back I was ready to frame the floor. I spread the liner on the frame and placed the already cut and prefit sill plate. For the sill plate I used treated 2x6s that I ripped in half on the table saw. With the sill plate dry fit in place, I used a drill and pre-drilled through the sill plate, through the pond liner and into the trailer frame. I spaced holes every 16 inches around the perimeter of the trailer. Once I had the frame pre-drilled I removed the sill plate and the pond liner and I filled every hole with roofing adhesive. Then with the aid of my friend scott hollis, we attached the sill plate. I stretched pond liner then put on sill plate foam then pressure fit the sill plate wood. I used the pre-drilled holes in the sill plate as a guide for 3" exterior metal tapping screws. I made sure every screw sinched down the sill plate and spread the roofing adhesive on the frame of the trailer.
Once the sill plate was attached I cut and fit in 1 1/2" thick xps foam. I filled all the gaps in the foam with great stuff and was ready to glue down the 3/4" ply floor.
I am leaving the skirt of the pond liner hanging around the frame and once the walls are framed and sheeted with plywood I will wrap the pond liner up and attach it to the plywood, but under the house wrap. Rain is the most serious concern when building in western washington, so I am taking extra care to make sure that the bottom of the trailer and the places on the house that are most exposed to rain will have appropriate coverage.