Floor insulation.

Next, it's time to prepare the trailer for the floor insulation. I started by vacuuming the bays, to remove all the leaves, dirt, etc.

Then, to make sure there won't be any water penetration from below (especially while driving on wet roads), I applied silicone caulk to all the seams. (I wiped them with an acetone soaked cloth first, to remove any grease or oil).

Here is the best caulk smoothing tool ever invented.

 I wanted to be thorough in the fight against water, so I caulked the fascia/trailer seams, and around the threaded rods as well.

The rigid foam insulation was recycled from a different project, so it came in pieces that had to be fit together in jigsaw fashion. I ripped each sheet on the table saw to the correct width for its bay (there were several different sized bays), then test fitted them for size.

Some of the insulation was too thick for the bays (which are 3" tall), so it had to be "planed". The method I arrived at, (with inspiration from LH), was to construct a jig with 3" tall walls, and cut across it with an antique 2 man saw. It took some elbow grease, but worked pretty well. (Sometimes, those old things in the barn are useful!)

The insulation was returned to the bays, and 5/16" shims were installed around the edges to maintain a space for the 1/4" nozzles of the expanding foam spray cans. The expanding foam will not only fill in the remaining voids, but also lock the rigid sheets into place.

 Weights were placed on the insulation to prevent the expanding foam from creeping underneath the sheets and lifting them (hmm, how do I know that might happen?) and then the perimeter of each bay was filled with spray foam.

It was colder than recommended for the application of expanding foam, so I borrowed a bucket of water from the hot tub to keep the cans warm.

The (nearly) end result:

I removed the excess foam, once cured, with a flat-bladed shovel after this photo was taken.
Next up: Sill seam, vapor barrier, and finally, plywood floor!