Luck would have it that the pocket exactly fit my 100-foot coil. If the fabric looks a little strange, that's because it's rescued from an old dress-shirt.
For a sense of balance, I made a second one for the opposite side, but lined it with plastic to make it water resistant. What I'll be putting in it isn't finalized yet, but at least I have options. My Singer had no difficulty with the plastic, but keeping the plastic from wrinkling proved to be an impossible task.
Nonetheless, hooking up the two pockets took less than an hour together,
Part 2 will cover sewing them to the trailer itself. All work done on my trailer an be found here.