Might I also suggest that the primary benefit of the SIP, which is its superior cellular insulation, is mere overkill in a teardrop trailer?
LONG REASONING: Insulation is critical in a home because it protects the heat stored in the thermal mass of the house. All the kitchen pots and pans, furniture, clothing, even the structure itself, acts as a passive heat engine when the air outside gets cold. Also, since a house is so big compared to a teardrop, heated air will remain inside the house for quite some time.
In a teardrop, the heating and cooling situation is totally different. Because its so small, the only real source of heat, passive or active, inside a camper is the human! And if you crack open a window or an exhaust vent, the cabin will recirculate its air every few minutes, not every few hours. In fact, in a teardrop, the main thing is to prevent radiant heat loss from the occupants to the walls and ceiling - and that honestly doesn't take a whole lot of insulation to make happen. In fact, just adding a 1/2-inch of rigid insulation reduces heat loss by about 3-4x!
It's not a bad construction technique, per say. I just worry you won't reap the benefits of your labor!