Gasoline heaters (or petrol heaters) are parking heaters that may be used as a heat source while living in your vehicle. They are less popular than diesel heaters, but may be a viable option depending on your vehicle and usage.
Disadvantages
Gasoline burns less hot than diesel, so the fuel consumption for a given amount of heat is going to be higher. Gasoline can also be more susceptible to coking/soot issues especially when run at the "Low" heat setting.
The smaller gasoline heaters also have more problems with high altitude. The manufacturer doesn't recommend running them above 4,900ft due to the extreme difficulties of sustaining combustion with small burners. Here is an interview with the company where they get into the details of why. They recommend that if you do plan on spending a lot of time at high elevations, to upgrade to the larger 4kw heater, and to make sure to run it hard.
Gasoline fuel tank tapping
If your vehicle's fuel type is gas/petrol, you may be able to tap directly into your fuel tank instead of needing to refill the heater's tank. Being able to run the heater directly off of the vehicle's existing gas tank is a huge convenience factor. Your tap should not go all the way to the bottom of your tank; this allows a reserve amount of fuel to be saved for actual driving. Some vans (such as the Ford Transit) can be ordered with an auxiliary fuel tank connection specifically for situations like this.
Maintenance
Just plan on having to clean/replace the burner every year or so.
Brands
Webasto is the major brand name in the market.
