alum took over the horse trailer market years back, BUT they are heavy even if alum! ha open car trailer doesn't weight squat! rust is issue with steel horse/stock trailers so alum is the choosen material IF a person wants to pay the price.
open car trailer, steel for sure IMO, I have had both wood and steel floors. some people claim the car will slid around on the steel treadplate floor but I never had the problem. I like treated wood floor and pour used motor oil over it o nce a year... works for me. I pull with a ton truck, but I feel brakes in one axle is fine.
I like 18 ft. 102 in wide, dove trail, if having it custom made I would go with standard FRAME AND HEAVIER AXLES, 6 lug rims. GOOD trailer spec tires. just me.
yep gooseneck pull soooo much better like he said, but cost more for sure.