Building a custom ultralight trailer - Part III - Lightweighting Strategies, or Challenging Your Assumptions

In the context of building a trailer, there are two major controlling aspects:

• Trailer features drive the size of the trailer
• Materials drive the construction techniques

In many ways, trailer lightweighting strategies borrow from the ultralight hiking community:

• Define your targeted activity
• Define the minimum basis set of capabilities or features needed
• Don’t pack (build) your fears
• Always pursue novel strategies for gear / construction

What do most trailers do? Well, most RVs are equipped to handle a family and provide a lot of creature comforts, a “home away from home”, as base camps. This makes them big, heavy, and not very mobile. Teardrop trailers are minimal little rigs that are nice for touring while you camp at established campsites with bathroom facilities and water. This makes them extremely limited in features. Campervans are designed to be minimal but self-sufficient movable homes that can access remote locations.

In my case, the target activity is: A trailer that can extend our hiking range by giving us a place to stay at remote trailheads and/or on the way back home. Thus, the trailer needs to be a self-sufficient, but minimal, home that is able to handle two to three nights of use without a resupply. It doesn’t need to handle a week; and it doesn’t need to be a home-away-from-home. In addition to being lightweight because we don’t want to sell either of our cars, light weight is also good for accessing remote locations. The trailer will be used primarily in summer, but could extend into shoulder seasons.

Minimum basis set of features: Start with a clean slate, and start adding in features that are needed, rather than taking a full RV (or other example) and reducing features you don’t need. In our case, we need a space tall enough to stand up in, that we can take a “Navy” shower in, that has a toilet, a bed, a table to dine at, a sink, and a burner to boil water on. It needs to be weatherproof and adequately ventilated. So what does that mean? Plumbing - water tanks (clean, gray, and maybe black), water pumping; propane fuel; a waterproof area.

Then what? Do we need a fridge? (Maybe… cold beers are nice after a hike.) A TV? (Nope!) An oven or microwave? (Nope and nope!) A furnace? (Maybe, shoulder seasons could get chilly at altitude.) A water heater? (Yes please.) Electricity? (Maybe, if we put in electrical items…) Lights? (Oh - yeah. Duh. So electricity is a must.) A separate dining area versus the bed? (Nope, convertible spaces are cool.) Does that toilet need to flush? (No, it can be a dry toilet - bye bye, black water tanks!) Will there be air conditioning? (No - way too resource intensive.) Will there be space for dogs? (Well, they can sleep in the trailer when we sleep, but they can’t stay in there when we’re gone.)

Construction techniques are probably the biggest place that people build their fears. This trailer will be moving down the highway at 60+ mph, going over bumpy roads… so the initial thought is to build it like a house+tank. Three-quarter inch plywood floor! Wood 2x4 framing! Screws everywhere!

Well… sure, you could do that… but it’s going to be H.E.A.V.Y.

Cue a piece of wisdom from a teardrop trailer forum. A wise person said, a trailer is more like a plane or a boat, not a moving house. Enter… marine and aerospace wisdom!

Guess what construction method is often used in these cases - not plywood with framing, but composites. Lots and lots of composites. Sandwich panels and fiberglass abound. Bonding happens with adhesives instead of screws.

What is a sandwich panel, you ask? A sandwich panel is a multilayer building panel that consists of a relatively thick layer of foam panel bonded on both surfaces to a thin layer of rigid, solid material such as plywood. The thicker the foam layer, the stronger the panel. The high strength-to-weight ratio comes from increasing the stiffness of the panel (by making it thicker) while minimally increasing its weight.

What about fiberglass? Fiberglass is a composite material consisting of glass fibers embedded in a polymer matrix. Strength is provided by the glass fiber, while rigidity is provided by the polymer (typically epoxy or polyester - more on that later). The glass can come in a woven sheet or a chopped strand mat (unwoven). Woven sheet is strong, while chopped strand mat is weaker but more formable. Fiberglass can be used to provide strength or simply to provide waterproofing. The more glass there is, the stronger and heavier.

DrBohr and I decided to go with a sandwich panel construction (edit: foam and plywood) with two layers of exterior fiberglass for waterproofing and structural integrity.

In the next post, I will talk about materials and component selection for our trailer.