If you suspect its the holding tank vent cap (plugged vent or reverse air flow when ROAD traveling) is the root cause, seriously consider the 360 Siphon product.
For more details, surf:
- Click Here - and
- click here - If wondering, I installed DIY custom made product similar to the Lil' Stanker (discontinued product) at
- click here - and never had internal stink problems again. And best of all afterwards, no need to buy toilet anti-smell chemicals again. Thus, my DIY custom built product paid for itself in 6 months.
In learning from above, I would install simple low cost roof top 360 Siphon product first, then (only if needed) install a new generation Lil' Stanker inline fan (re:
- click here - ) next. Lil' Stanker inline fan would be great solution on no wind days.
Pushing or sucking bad smells out its roof vent works great. Wish it was minimum build on all RV trailers.
Hope this helps.