My back-up is gas powered but was looking into converting to propane, but not really sure if the engine would like it.
Some say it's better others say not ,who do you believe?
The only consistent "downside" I hear with running a petrol (gasoline) engine on propane is upper-cylinder lubrication issues.
My own case, I took a standard 4-cylinder, 16-valve, double-overhead-cam engine, removed all the fuel injection nonsense and added single-point gas injection (mixing). I've seen unbelievably good plug condition, oil remains in very good condition for ages, and apart from oil (and filter) changes every 400-500 hours (equivalent to about 40,000km highway driving), and changing plugs about every 200,000km equivalent, it hasn't been touched.
To address the upper-cylinder lubrication, I vent the rocker cover to the air/fuel inlet after the air filter. The very small amount of oil fumes there seems to do fine.
I've had the oil analysed a couple of times and it shows no excessive wear and no other problems. No performance problems.
Here's a sparkplug after the equivalent of 200,000km (running on pure propane)
Here's under the rocker cover - oil hasn't been changed in 500 hours (around 40,000km), the engine has done in total close to 400,000km (equivalent) here, nothing apart from oil and plug changes.
Apart from slightly harder to start, and slightly less power (not an issue for me), there isn't any downside to the conversion, just do it!