[aerohead]

There was just enough information to reverse-engineer some values for the semi-trailer:
Length- 576" - 636"
Height- 162"
Width- 102"
Ground clearance- 9.1"
Skirted wake- 93.5-sq-feet
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If 0.175 = 26% drag, then the rig without any mods is Cd 0.67307
With gap-seal and lower skirts, Cd 0.5953
With gap-seal, skirts, and tails, Cd 0.52607 - Cd 0.49807, delta Cd 0.028 ( 5.32% )
If the four tails are extrapolated out to their terminations, they form 'complete' tails of 128", 145.4", 229.6", and 263.3".
With 48" tail with 4-sides, estimated Cd 0.452
With 60" inflatable tail ( longest allowed by DOT ), estimated Cd 0.4185
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@ 65-mph, the drag -to-mpg relationship is delta-10% Cd = delta-5% mpg
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The following boat-tails, if sized to match the Lawrence Livermore semi-trailer width produce lengths of :
1910 Maurice Farman strut ( best ) 145"
1922 Jaray square-cylinder............ 129"
1933 Frey 2D section ................... 141.4"
1963 Walter Korff semi-trailer......... 191.7"
1969 W.A.Mair torpedo................... 193.8"
1976 Wysocki railroad tail.............. 163.2"
1981 NASA Shoebox ( ave. top/side ) 113.4"
1981 NASA semi-trailer.................... 146.2"
2012 Breidenbach SUV..................... 258.6"