The Sonos play 5 is a very nice speaker for a larger room, I had one but recently inherited a second so set them up as a stereo pair and they sound awesome. I only use spotify and its ample for me.
Maybe a piece of decent quality rubber fuel hose with the correct clips, 8mm inside diameter would be a good tight fit on it and although its plastic it should be ok. Not sure how the Mot man would be with it though.
I have 2 of their jacks and touch wood have not experienced any issues in 5 years, personally i would look elsewhere though from what i have read online about them.
Im of the opinion that when its brakes involved then replace the carrier.
I have had very little experience with inserts but have heard timeserts are the ones to go for for strength.
The seller will always cover themselves by saying its for test purposes only, these things normally just plug in instead of the occupancy mat and give the system the resistance it needs to see. I have not looked at the listing but i would guess its telling the car the seat is occupied at all...
The Noco ones look really good and where i would put my money, thought about getting one with an inflator built in too but not sure when i would use it!
I think I would have a go at sealing that myself with something like JB weld but make sure its fuel resistant.
Obviously empty tank and cleaned up as best as possible first.