Nidokoenig

That's the problem: Weapons are blocked from using some of the enchants apparel can(and that perks can, for that matter). The drop down menu for weapon enchants doesn't include the StealthBoyInvis effect, as the OP described. See pic for what happens when you switch an apparel enchant with stealth to a weapon enchant. I'd love for someone more experienced to demonstrate otherwise, but my tomfoolery with scripting and hidden perks seems to be the simplest way to make the game behave as if the weapon is cloaking the player.

You could add a stealth perk and script it to to be added on the item being equipped. I messed around in the GECK and was able to do just this: http://www.fallout3nexus.com/downloads/file.php?id=7636 When equipped, the item has a script which adds a perk which adds an effect which adds a stealth field if the player has a weapon out.

I did some searches using "car" and "resource", but the closest I could find was this: http://www.fallout3nexus.com/downloads/file.php?id=7133 Look essentially like a vanilla car, just fixed up to be drivable.