I've personally never come across using a marinade as a specific preservation technique, not with oil anyway. Something like honey would create a good antibacterial barrier, or good old fashioned salting (just remember to soak it out a few times) would also happily do the job.
If you were to use an oil, and it's likely to get warm/aired, I would coat with a good coconut oil. Firstly it won't go rancid being sat around, and secondly it's also got antimicrobial activity.
Fat burning is affected most by omega 3>omega6>monos>sats.
All oils carry 9kcals per gram. MCTs from the likes of coconut oil, or lesser extent butter, are metabolised extremely efficiently and can't themselves be laid down as fat.
Sat fats should be eaten away from refined carbohydrates, beyond that, they are not the devil.