The Duck's Tankers
There were 2 trailers used for the movie, both were identical 1960
Trailmobile model T4-02-22 insulated tankers, with a 5800 gallon capacity.  
One of the two trailers was blown up on the bridge, and the second trailer had
Missouri and restored.

The surviving trailer was used with the 1970 second unit truck, but did get
pulled behind the 1977 Mack in some of the final bridge scenes near Mint
Road. Most notably, you see this trailer on the rear of the truck as the first
explosion from the rear takes place after being shot by the two kneeling
officers.  Note the trailer had a hole cut in the bottom rear to gain access to
the inside of the trailer.  Originally an asphalt tanker, this surviving trailer had
its structural insulated main tank removed, leaving only the aluminum skin.  In
order to hold the skin in-place, a web of steel strengthening was installed
inside.  According to multiple sources, the primary reason for this
modification was to eliminate as much of the trailer weight as possible,
maximizing the acceleration of the Macks.  Also notice the damage to the
passenger (right) side hose tube sustainted when the trailer hit a support
column as it crashed into the jail.  We're restoring the trailer to "as-filmed"
condition, leaving the webbing inside and the damage to the exterior from the
jail house.

When the movie was filmed, the trailers were painted with Rust-Oleum
Aluminum paint to hide the asphalt streaks down the sides and on the
underside of the tank.  The caked-on asphalt can be seen in the movie on the
tire carrier and rear suspension.  We have painted the trailer exactly as they
did in 1977, keeping the original tar in-place.

The original decals were still in-place.  Detailed reproductions were made
from digital photographs.  The new decals were placed exactly as they were
when we picked up the trailer.   A complete new lighting system was ordered
from the original manufacturer, Betts Industires, and all lights were replaced
with new, original-style lighting.

Those that have seen the trailer in-person will notice that the brake drums and
shoes are missing.  The shoes and drums were removed once the inner steel
tank was removed to prevent the trailer from twisting or bucking from stress
due to trailer brake force.  As the trailer now only weighs approximately 3000
pounds, there tractor's brakes are more than sufficient to safely stop the truck
within all applicable federal guidelines.
All that remains of the other Trailmobile tank trailer after the explosion is the rear
suspension and tail assembly.  
This is how the trailer in May 2008 looks after restoration to its as-filmed condition.
good condition after sitting for 30 years in the New Mexico desert.