and a survey of 1/72 scale tanks in various kits here:
Freightdog (http://www.freightdogmodels.co.uk/) is now producing 1/72 150-gallon and 300-gallon (finned and bobtailed) Douglas external tanks as well as the D-704 refueling pod. Colin sent me samples and they look really good, both size and finish. Note the separate and finely molded turbine on the D-704:
Pablo Ziegle called my attention to another 1/72 option for 300-gallon tanks from Attack Squadron in Poland.
Hannants is listing them (http://www.hannants.co.uk/product/ASQ72014). Each set includes three tanks and the fin options for each. Pablo is awaiting a set so he wasn't able to comment on the accuracy or quality.