Hello Jack

Pretty much all of the LPU's are similar which is what the high end aircraft
paint is.  And in spite of its high cost, most airlines use it due to it's
superior toughness and down time on the heavy iron is about $80,000 per day
so it pays to keep them flying.  Car paint is not normally of this variety
but it can be.  And also, you can have a urethane that isn't cross linked.  
The cross inking adds toughness and gloss retention by having a molecular
bond that is more resistant to the light spectrum in the UV frequency.  So
this cross linking prevents molecules from sliding around due to them being
"knitted" to adjacent molecules.

I like US paint's "Awlgrip" but  International Paint's "Interthane" and
Sterling I think they are all pretty similar.  I haven't painted with Imron
for awhile so it's formulation may have changed but I found it a lot harder
to apply and by virtue of it being an aromatic urethane vs. the aliphatic
variety of Awlgrip, Sterling and others, it seems to have a bit less gloss
retention.  One of my past boats I did in metallic Imron trim on top of
Interthane so I got a good comparison but even that is flawed in that
different pigments fade more quickly than others.  So for what it's worth,
I'm staying with Awlgrip.  I wouldn't go with car paint since I haven't found
a standard paint with either the gloss or color retention of LPU's.

Dan Newland