Most reputable brands offer similar performance in terms of alarm threshold values, decibels of the alarm, etc.
For surface-mount, pick wichever model you like, but for a recessed mount, make it easy on yourself and use the same type you had before, so you don't have to cut a new hole for it.
You can get models that include an automatic shutoff valve (Safe-T-Alert makes one), that shuts off your propane when a leak is detected. That's probably overkill for many of us, but good for people who will be away from their trailers for a large chunk of the day with propane appliances running. However, even the models with automatic shut-off valves won't open your vents and windows for you. They won't get rid of the LPG concentration that originally set off the alarm; it will only keep matters from getting worse.
By the way, at least one Safe-T-Alert model with automatic shutoff valve is a combined LPG/CO detector. If you use one like that, you would still need a separate CO/smoke detector, because LPG detectors need to be near the floor and CO/smoke detectors near the ceiling.
And just to round out the info-dump, the biggest hazard with LPG isn't explosion; it's inhalation. The concentration of propane in the air that's hazardous to your health is only about half of the Lower Explosive Limit. So propane can hurt you long
before it can blow up your trailer. Since propane tends to settle near the floor, you're most at risk of getting a lungful of the stuff while you're sleeping and your breathing zone is closer to the floor. But it's especially hazardous for small kids and pets whose breathing zone is always
close to the floor.
On the plus side, a good propane leak should kill any mice infesting your trailer when they
get a lungful!