A quick estimate shows 12~ square feet of aluminum-to-aluminum contact from the ribs/bows onto the interior liner panels on my 27', then start adding it the cross-bracing & floor c-channel, window and vent opening frames and the number jumps to 40~plus square feet. With the heat-transfer ability of aluminum there is the place to retrofit in a solution.
Aluminum has thermal conductivity of 220-255 mW/m-K so ANYTHING placed to reduce the flow there is money well spent. It's a matter of porportions, it does not have to be the extremely low 0.035 - 0.16 conductivity of common insulations or the 0.003 (!) performance of aerogels. CanoeStream phrased it correctly, rigid and structural properties researched carefully to not allow the binding points of rivets to loosen immediately and progressively worsen as the material creeps.
With aerogels it seems every wants to sell value-added products, housing or commercial structural panels or drywall with the gel added, etc. - for custom rehab work unless you are buying a 5-gallon bucket of loose 3-5mm granules it's best supplied in 5 or 10mm thickness rolls resembling felt.
There are 58" wide rolls available with or without a foil backing that could be a category killer for sure - four 10mm layers would fill the cavity 100% on older trailers, and using it to insulate only the ceiling and the top curve of the shell would catch both sun loading and the majority of heat loss for cold-weather use.
I've run the numbers a couple of times for my own projects - IF I was neck-deep in a 2002/5 or newer trailer, or a true heirloom vintage unit that held a better core value, I would be trying to line up some aerogels...