Well, the good news is Round2 is reissuing the Freuahuf 40ft Van trailer later this year, so you should be set there.
Now, ready for the bad news? The AMT "Movin' On" Kenworth is not even close to correct. The kit is AMT's 1968-1972 Kenworth W923 (or W925 if you're lucky enough to get the torsion bar suspension) with some "Movin' On" looking decals thrown in the box. The actual truck used in the show was a 1974 Kenworth W900 with a VIT interior.
So, if you want to make an accurate "Movin' On" Kenworth W900, here you go. First, you'll need the cab, interior & sleeper from the Revell of Germany W900 or T900 kits. Keep the hood from the AMT kit.
Second, you sort of have a choice of engines as there was more than truck used for filming. You can either use the NTC350 from the AMT kit, or you can use the Auslowe Cummins VT903 (which is what the truck had if you asked Sonny). For this year Kenworth the engine should be white.
Third, In order to fit the 60" sleeper, you'll probably have to streatch the frame. You'll also need to get a set of the Tandem Torsion Bar suspension. Eric Jones (aka Porky) offers it in resin.
This might help, too:
http://timstrucks.site.aplus.net/images/images_oct/sonnycolorchart.jpg