Is an air tank required?
Could an air tank fit in an Expedition engine compartment?
Can an air tank be long and narrow?
But how could I face a horn forward?
Do they have horns with 90 degree bells?
If so, I would mount it lengthwise across the radiator behind the grill, 45 degrees downwards to drain water.
While at Walmart, buy their LED penlight. $4.88?
Bright, compact, handy, batteries last forever.
Now if it could just have a built-in pen so I need not also carry a pen in my shirt pocket.