Have you given any thought to what era or RR you want to model? Early cans (containers) were mostly 20', 40, & a few 45' cans for foreign goods (Asian & European). Later when they were used for domestic loads 48' cans & wells carrying those. Nowadays most domestic loads are carried in 53' cans. Most if not all 48' wells are now only 40' long for mostly foreign loads. And nothing says a few pigs (trailers) can't be thrown in the mix.