That is a beautiful rig you have there. I think any color that you put on it will only make it more amazing.
Are you looking to go solid colors or are you wanting to do airbrushing? Like flames on the smoke/heat box and maybe some other mural on the barrel smoker part.....
I am not an artist but I know there are a lot of gorgeous trailers on TV and on the internet, perhaps you can pull the best you like from different ones. Maybe even paint some sort of long round smoked meat on the barrel and flames or something related to what you put on the barrel.
I know that probably does not help much but again, whatever you do, that thing will be even more amazing.... Gives me something to look forwards to in the future..