rather than the petroleum jelly alone I suggest you use a layer of cling wrap over the vehicle which you adhere with the jelly if you like and add a few dabs on the other side to make the paper adhere to the cling wrap. that way you know you won't be stuck on the car. as both the jelly and the cling wrap will let you move the shape hither and yon.

I wouldn't mache the windows as the undercuts would present problems on a VW. Leave them open and you can add a sheet of something later on.(but reinforce the rims with some insert like bamboo skewers...)

I don't think you'll need reinforcing like wire overall.

It's tempting to plan to slice the thing in two at its completion to get it off the vehicle. to do that you can run  a line of tape or plastic affixed vertically from the front to the rear end or some other spreader divider as the strength you want may require you to make the shape stiff --so stiff that you may not be able to get it off. i'd also do the mache with the bumper bars removed and the wheels done separately. build the bumper bars and number plate out of a separate job.

when you join the two halves you can do some more work on the thing but at that stage you may want to consider some form of reinforcement. the problem is deciding how many layers you need to do in situ before you take it off. if you use kraft paper you could get away with less than if you used newsprint.

when you put the wheels(they'll be half wheels I guess) back "on" you'll need a way of fixing those so that they ride at a distance from the mudguards. So that suggests that you need some inner support to hold the car chassis  off the ground --so you'll need a structure of sorts underneath. Another way woudl be to take the mudguards off and do the whole thing (with the wheels)that way before later putting the mache mudguards back on... if you did it that way put some structural support in the wheels as they will be carrying the weight.
also remember that when you put it back together you will have to reach over the caST to cover and join it. thats' possible .  Also you can use masking tap[e for your join and then mache ovewr that.

I think on a Vdub but you may have to test it out firsts.

dave riley

wow, great reply dave, sorry about the slow getting back.  we have started the vw with vaseline only (wish i had read this earlier, cling wrap sounds wonderfully effective) and are actually going to split it head to toe and do vw "halfs" on teams to be displayed on the wall.  hope it works.  appreciate the tips on the wheels / tires too, will be doing them separately.

more later
thanks
darren