Sometimes I'm glad I grew up working on furniture!
I am in the re-planning/pre-construction phase of building a squared-off TD modual, that will slide on and off a harbor frieght trailer. And one of the easiest things for me to plan, was how to fasten the modual in place while its on the trailer. The trailer, in its basic utilty configuration, will have a 1/2 inch plywood deck, supported by 1-bys or 2-bys on the frame itself. When the modual floor is first laid out, 6 bolt holes will be drilled thru the modual floor, thru the deck of the trailer, and thru one of the supporting 1 or 2 bys. Then simple T-nuts will be driven into these holes from the bottom of the frame.
To secure the modual for transporting, bolts would be run thru from the modual floor, thru the trailer floor, and into the T-nuts, allowing the bolts to be tightened from inside the modual, instead of needing to crawl under the trailer. And with the modual removed, shorter bolts would be placed in the holes and tightened, to keep debries from things being hauled from going into the holes and blocking them up. This way to go from trailer to camper would mean removing 6 short bolts, and replacing them with 6 longer ones for the modual. In fact, if ground clearance and under trailer snagging are not an issue for you, like they will be for me, then the same long bolts can be used for both situations. That would save keeping track of 2 sets of 6 bolts.
Far as getting the modual on and off the trailer, I'll be puting eye-bolts thru frame members at the front and back of the modual, at the corners. This will let rope, chains, or whatever, be hooked to the eyes, to safely pull the modual one way or the other. Such ropes,chains or whatever can be hooked to a convenient tree or a stake in the ground, to hold the modual, while the tailer is slowly pulled out from under it, to take it off the trailer. And a small winch on the trailer tongue can be used to pull the modual onto the trailer.
I designed it this way, for minimal effort in getting the modual on and off, to save strain on my back. And also wanted a modual, so I can get to the campsite, drop off the modual, and go off with the car and trailer to get some firewood. When I get done unloading the firewood, I can pull the modual back on the trailer. and be all ready for a weekend or a week of camping, with plenty of wood for the campfire.
