I haven't ever cooked in my clipper while traveling - I don't use a slow cooker, instapot, etc. I also don't drive with my propane on.
However, if I did cook while driving, putting the slow cooker in the sink would prevent it from flying (heck I already put a teapot in the sink while traveling and it has never flown out). This also prevents anything inside the cooker from spilling out onto the floor - everything is contained in the sink.
If I were in a situation that could cause the slow cooker to fly out of the sink, then the slow cooker is the least of my worries. And for that slow cooker to fly out of the sink and get all the way to the other end of the RV in order to dump it's scalding contents on me... well let's just say I wouldn't put any money down on that happening.
I would not use my oven while driving simply because a sudden stop could potentially have the contents flying out of the oven or spilling in the oven which could potentially cause a fire. My oven is propane and uses a flame. The slow cooker is electric, the outside never gets hot and it is built so as not to tip over in normal circumstances - putting it in a sink or even metal tub on the floor would be enough to keep it secure.