Howdy Patriot,
Well I havent built the challenger2, but, if you enjoy tanks and armor, I do have a few links for you, that you may or may not have seen. They are all free downloads.
http://3dpapermodel.w-web.com/3dpms/Alvin/alvin.html#leopaprd2 this is the leopard II MBT (man battle tank). Its a 3.5 MB .pdf and looks very nice.
http://www.konradus.com/szufladki/agand/index.html This is a 1:25 scale M5 Stuart VI, its really nice looking.
http://www.advstudio.com.hk/paper-pro/new/eng/eindex.htm There are two models on this site, the Panther tank and the tiger tank, In the right column, scroll down, they are the last two photos/files. The TIGER tank kit is an especially GREAT looking model when finished.
http://3dpapermodel.w-web.com/3dpms/civi/civi.html#jeep Here you will find a nice WWII jeep.
http://www.stdcomp.com/485tmw/model.htm This is not quite along the same lines, it is a MAN Tractor and TEL cruise missile launcher that was phased out by the salt II treaties, designed by Ron Caudillo who made it for fiddlers green and has offered it as a free download for the 485th Tactical Missile Wing Alumni Association. It is somewhat similar to the Patriot Missile Battery and I thought since you have the name Patriot Missile, you might find it interesting.
http://www.terra.dti.ne.jp/~yoshidom/ Last but not least, here are alot of 1:72 scale model tanks and armor. Not all are available as free downloads but there are some like the Panhard AMD 178 armored car, BA-6 gun truck, M4A3 Sherman, Churchill Mk3, Strv.103B, Hunting Tiger, T-34/76 (M1942), Pz.Kpfw.IV ausf.G , M60A3, MerkavaMk3 , and a few others. However, being 1:72 scale, they are small, and are what is known as "white kits" (no color). You may however be able to enlarge them and color to your liking.
As I said these are all free downloads and I am assuming the various sites are the copyright holders of these models. But I hope that if you enjoy armor, these will give you something to do once you finish the challenger.
Have a nice day,
Greg aka GEEDUBBYA(GW)