My message wasn't complete.

I have used household type 12v halogen lamps in my vanagon (good cheap
replacement for my 84 westy house lamp)  with no problems at all.

Carefull though, if you add extra lighting: halogen lamps get VERY HOT,
hotter that your typical household bulbs and therfore could create fire
hazard or sipmly the risk of damage to the interior of your van.

I had set up a brake light bulb in my westy side tent. It was accidently
moved into contact with the roof and it burned a hole right through in very
little time, despite sub-freezing temperatures outside.

Fred