eventually i've found something to suit, waterproof and non slip too, it's a gland grommet apparently so it's fixed to the bulkhead and where ever i put the wire it won't pull in or out when i tighten it up

plus it's waterproof x2, both on the outer bit where the wire goes through and the bit where it joins onto the bulkhead, water won't get there unless i run a hose in the engine bay but better to be safe than sorry