I'm going to attempt to fix my problem of re-fuelling issue by looking at filler hose and vent hose while also changing the charcoal in the canister while the bed is off.
my question is, what type of sealer do I need to use to seal the end cap of tje charcoal canister?

 

Hum... never seen anyone try to fix a canister. If I were in your shoes I'd contact permatex and ask them what product would be best.

IMO.. just buy a replacement canister. (but I do appreciate someone fixing things themselves and saving $$)

 

agreed, i would probably use the black RTV thats oil and gas resistant and call it good. Does need to be vacuum tight remember so make sure its well sealed.