Floor is aluminum with stud sized crossbeams running under it. 7' wide x 20' of foam plus a V-nose... Foam is 4" deep and covers the studs. I had them leave two bays open for water tanks. Estimated foam is about 600-700 board feet. They also sprayed a fire retardant barrier as the last step.
Total cost was $1550, or $2.50/board foot.
It took them three business days plus a weekend in the middle to get it done, and I left the trailer at their place. The internet says closed cell spray foam should cost $1.30 to $2.90... so while expensive it wasn't completely nuts. I called around and of the five companies that did trailers, only this one was able to get it done in less than 30 days notice. Getting spray foam kits for "DIY" from Home Depot was going to be similar price plus a big hassle.
We have some high elevation cold weather camping set up for spring break, we'll see how it fares. Previously the metal floor got very cold and just sucked all the heat out of the trailer. With hookups we could keep it warmish inside but off grid if you weren't running propane continuously it get awfully cold.