Re: Smoke and CO2 detectors
Double-sided mounting tape, and a BIG patch of it, will work. Most "Velcro" adhesives will release on a hot summer day.
Also be aware the all of the inexpensive smoke detectors are "ionization" types that need to be thrown out, completely, in five years. They tend to die around the 5-7 year range as the ionization chamber gets covered in crud internally, and if you are in a salt air location, I'd expect it to fail even sooner. So look for a "dual" detector, because the photocell type are slower on some fires, faster on others, and the dual detector can sometimes give you a full 15 minutes of additional warning. Figure $30-50 for a dual detector, and keep the CO detector separate. Those also fail over time.
If you aren't really sure of the difference between CO and CO2...take a basic boating safety course with the US Power Squadrons (USPS) or similar. You'll appreciate some of the safety tips, and probably get an insurance discount when you renew.