Ashley,
If the odors are
holding tank related, you could consider going to a so called composting
toilet.* They are actually desiccating, but many of the folks who have them swear by them--and the eliminate the
holding tank odors issue completely. Here's a link to one of the CF threads about them:
https://www.cruisersforum.com/forums...-250159-2.html. If you want to see more threads, use the CF Custom
Google Search, under the Search button, and enter <composting toilets>. There will be a few different threads about them.
* If the odors have permeated the
fiberglass, they have also done in your
cushions and their covers. Wash all with a strong bleach solution.
Cushions can be soaked and washed in bathtubs, and they need to be vertical to drip and eventually dry. Sunlight is okay. The bleach smell will fade. It IS an opportunity to make new covers. Take the dimensions from the cushions. Make them easy to remove (I like to run the zips around 3 edges, so that they are really easy to do.)
If the horrendous smell is not related to the holding tank, giving us an idea of what you think it
might be will help us decide what to write. For instance, getting rid of
mold is a different problem from getting rid of
diesel odors. Do be aware, the smell could be from mixed sources.
Sorry for your woes.
Ann