Our 2005 Bambi came with two regular roof vents. I had the Airstream dealer install one FantasticFan, which left one regular vent. A couple of years later, we were boondocking on Lone Rock Beach at Lake Powell in the summer; and I realized that we would have been a lot more comfortable with a second FantasticFan. So, a couple of months later, I replace the remaining regular vent with another FantasticFan, myself.
I was hesitant to enlarge the hole in the roof, because cutting holes in the roof panels just seems wrong. However, when removing the old vent, I discovered what a hack job the factory had done installing it; and I decided I couldn't do much worse, even if I tried.
Once you get past the first cut, it's not that difficult. I did purchase some right-angle sheet-metal shears, which made the cutting much easier. Just remember to measure twice and cut once. (Funny how those old sayings can take on a new, deeper meaning in your old age. However, sometimes they just mean exactly what they say...)
Labor doesn't get much cheaper than free. And, if you do the installation yourself; at least you'll know who to blame, if it leaks.