Generally speaking, anything that falls inside the body of the car is
'shadowed' by the metal around it (remember the Faraday experiment?).
The headliner edges, depending on where you put the antenna(e), could be
particularly bad, again, because of the 'shadows'.  One alternative could be
along the inside top edge of the pop-top.  This would give some clearance
above the metal, and would not be visible from the outside.  Unfortunately,
it would still be a horizontal loop....  It might be worth a try...

Cetin

BSNICH01@ulkyvm.louisville.edu writes:
 > Thanks Cetin.  How about if one could arrange a loop or antennae
 > INSIDE the van.  Maybe like in the headliner and edges of the front
 > windshield and down into the nose?