As long as we are talking about trailers, you might also want to consider a pop-up style camping trailer. You have seen them, the ones that fold down into a solid box with a trailer hitch for pulling with essentially any type of vehicle equipped to haul a trailer.
They have canvas sides, with a solid floor and roof. Once collapsed they cannot store a lot of supplies but there is some storage capacity, however, they are a shelter and are typically equipped with a propane stove, lighting, sometimes a small refrigerator, Porta Potty, and bunks. The refrigeration system would require electricity hook-up, and/or you would need a small generator.
Your typical cargo trailer that is not enclosed can be used to haul extra fuel for your vehicle, water, and other supplies and can double as a shelter when tarps are used. Trailers with metal mesh type sides are ideal because the sides help keep supplies contained when traveling, can be secured against theft to some extent, and makes stringing a tarp for protection from the elements much easier.
Your supplies carried in an open trailer would need to be covered with tarps to protect them from rain and snow. The tarps would have to be secured properly to keep them in place as you travel. Some people tend to underestimate the force of the wind against the tarp as the vehicle moves down the highway. The drag can be tremendous, so the tarp must be of good quality and secured properly.
Fully enclosed trailers similar to box trailers used to haul household goods with a door that can be secured with a lock are a step up from an open trailer bed. The enclosed trailers protect your supplies from the rain and snow and from theft.
There are trailers that are designed especially for bugging-out. You have to keep in mind your trailer will need to be able to go where you go, or more specifically where your vehicle can go. If you have a four-wheel/all-wheel drive vehicle with a high ground clearance, then you have to ensure your trailer has the clearance and the tires to accommodate the rough terrain.
The so-called survival trailers are expensive. They can run into thousands of dollars because of the customizations. Do you need a customized trailer? Remember if you plan to use your trailer during a bugging-out situation, you may end up off road. A loaded trailer with factory wheels/tires and suspension may not be adequate for the terrain you may encounter.
You may need a heavier suspension with shocks in some cases along with tires suited for rough terrain. Some trailers come equipped with platforms for tents and sleeping areas and have special cargo holds for carrying fuel on the outside of the trailer. Fuel should never be carried inside of an enclosed space without adequate ventilation.
Weight and fuel efficiency is always a concern so make sure your vehicle has the capacity to haul the trailer with its expected payload. There is the weight of the trailer empty and then the weight of water, fuel, and other supplies on board. The weight adds up quickly, so you have to base your vehicle’s capacity on a fully loaded trailer and not on the empty weight of the trailer.
The color of the trailer may become an issue if you want to hide it. The standard utility trailer is usually black, while horse and other enclosed cargo trailers are typically white. You can paint it any color you want or have it customized, but consider concealment when choosing a color.
Leave room in your trailer for sheltering, or at the very least pack the trailer so some items can be easily removed for sleeping and taking shelter. This means some supplies may have to be stored outside the trailer during bad weather and for overnight sleeping. Be prepared to secure and cover your supplies.
Some people have converted small and then not so small horse trailers into camping trailers. This will, of course, take some skill and financial resources on your part. If you already have this type of trailer you are ahead of the game, and can convert it at your leisure and as funding allows.
Your basic needs would be a place to sleep comfortably and have room for supplies, have a vehicle that can haul the loaded weight, and that the trailer can take some rough terrain.
Back to the question of whether you need a trailer or not for bugging out, or for bugging in for that matter because a trailer can be a refuge, and be an additional storage space on your property for supplies. A trailer well hidden and secured could be considered a supplies cache if done properly. The choice is yours based on your survival plans, family wishes and finances.
In a perfect world, you would have a trailer parked in the garage loaded with emergency supplies ready to be hooked up in a matter of minutes to your bug-out-vehicle. However, when is life ever perfect? One problem is deciding what to pack in your trailer because the more cargo space you have the more you will load it up with things you may not necessarily need but simply want.
You do not want to head out with an overloaded trailer and then have to decide what gets left along the trail because your vehicle is overheating from the weight, or that your reduced fuel efficiency is not sustainable. Overloading your trailer can cause problems with the tires, wear and tear on the vehicles transmission, and then there is the safety issue, which must always be considered first and foremost.