My antenna is in pretty much the same spot, only drivers side and I'm able to hit a repeater a good 40 miles out with it in this location using the Midland MXTA26. I also placed it here so I wouldn't knock the S@#% out of it loading and unloading things on a roof rack. Also powder coated like yours. I'm very happy with mine.
For comparison I am running three times the wattage as you and the repeater is on a mountain with good line of sight so as they say your mileage may very but I think you'd be happy with the MXTA26. I'd say try a better antenna or relocate the one you have to a higher spot.