I'm a fan of what Scamp
uses: foil bubble wrap, available at big box home supply stores or online, followed by carpet style marine headliner, available in a range of neutral colors online or through a local marine supply store.
It's not as thermally efficient as the original Ensolite, but it's reasonably priced and fairly forgiving to work with as a DIYer. The headliner is slightly stretchy, which helps to get it to fit smoothly in the corners. Install with automotive headliner adhesive.
It does what it needs to do in terms of preventing condensation, deadening sound, blocking light
, and adding a modicum of thermal insulation. It's also soft to brush up against (which happens a lot in a small trailer) and cleans with a vacuum, damp rag, or steam cleaner as needed.