Not sure if this will work for you but these are a couple tricks I've used over the years:
A plate of coffee grounds ( unused ) will absorb a number of smells. I think the absorption of the smell by the surface area of the grounds is the trick.
An old car dealers trick for cars that have been smoked in for years is to cut an apple in half putting the halves under the seat. Close the doors and windows and voila, in a day of hot sun the smell is absorbed by the apple.
I have a mesh bag of absorbent clay that sits onside the holding tank
. Monthly I take it out and after a day in the sun it expels the odours. I replace it by the tank and have never had a noticeable smell, ( at least not noticeable to me but I might have gone, "Nose Blind" ).