remote start external antenna?

I'm currently building up enough knowledge to install a car alarm/remote start. It's a NIB "Zenesis" Z402AS (2 way) I picked up for a great price. It's actually just a re-branded "Easycar" system. It's going into an older 1998 GMC Fullsize pickup so it's not going to be an overly complex job. I'm just looking for better RKE range than the 3-odd feet the OEM unit gives and the remote start for winter. My question is regarding the Antenna. It's a 433 MHz unit and they claim "1 mile reception". Yeah, maybe on a perfect day across an open field, with me standing on an 8 foot step ladder with brand new batteries in the remote....maybe. But I digress.....to the question at hand: My truck has a hole in the roof dead center from a CB radio installation that is no longer in use. It's currently sealed by the original CB antenna mount. I was looking at that hole and wondering if there would be any advantage to using it to mount the alarm/starter antenna through the roof. Antenna close to vertical orientation of course. That's the optimal location for a CB antenna to maximize both transmit and receive range, although I'm not sure it translates directly over to a 433 Mhz antenna. That's quite a bit different spectrum than CB at 27Mhz. But I can't help but think that getting the radiating/receiving antenna up above the steel body would be beneficial. The high mounting would also probably help signal receive/transmit in all directions at there would be no steel body shielding the signal. The cabling for the antenna module is long enough to reach just fine as is, so no worries there. Obviously, A weather tight casing would have to be used around the antenna itself since it's designed for interior mounting. Making a casing is pretty simple. I can either construct something myself or re-purpose something commercially available like those shark fins or something. I'd also have to make sure it's not going to hit anything if up there. I doubt it will survive a brush with the garage door frame let alone a "whack" at 55 MPH. So, am I wasting my time or does anyone think I will get better range/response from mounting the antenna outside the vehicle body? Cheers

It sure couldn't hurt to have the antenna placed as such. You will need to come up with a way to keep it weather-tight and you of course then have the issue of having to mount the module up in the roof of the vehicle. thankfully it is a separate antenna receiver module and you don't need to put the entire brain there. you might even be able to build a "housing" using some pvc conduit which is weatherproof and you can get various fittings and make it easily attachable to the roof in the existing hole. Let us know how it works out.