...with all due respect to the other posters, it sounds like you have an odor problem with a cause, one that should be ferreted out, not masked.
If it's mold or mildew, it will smell earthy, dank, dirt-like, if it is black mold; and yeasty like parmesan cheese, if it is white mold. If that is the case then there it is possibly a water leak somewhere (check: shower sunlight, shower undertub plumbing, sink plumbing, roof, slide-out, A/C system?). You will need to search relentlessly until you find it.
If it is some other funky smell, then I would suspect that you have "bio-slime" growing in your P-traps (. If you have a keen sense of smell, put your nose at the throat of each sink and take a good whiff.
As you know, there are typically 3 P-traps in a Travel trailer (bath sink drain, shower drain and kitchen sink drain). There are enzymatic formulas you can buy at Lowes in a large 32 oz. container to treat P-traps and kill that bio-slime.
However, in a pinch, you can just mix up some rubbing alcohol and 3% store-bought hydrogen peroxide, with a small amount of dish detergent and pour it in there. About a 10 oz. per trap should do. Do not use this in conjunction with bleach, but separately, as this would create an adverse chemical combination. Let this mixture sit in the P-trap for a few minutes then follow with a hot (not quite boiling) water flush to remove the bio-slime. Some grayish-black slime will end up in the grey water tank, so you wont see it, but the smell should be gone.
We also use the Starbrite RV deodorizers with Sodium Chlorite. This product, when exposed to humidity, releases chlorine gas vapor to kill off any mildew or mold spores that are so common in RVs. Starbrite used to sell these in a sachet that lasted for months with several ounces of the powder in it - I bought a case of them once a few years ago - but, the current version is 1/20 that in volume and they do not last as long. Why they scaled down their product and made it less useful and long lasting I do not know, but do not expect the current version to last for more than 2-3 weeks. Plus, to cover a large travel trailer or 5th wheel, you would need to get at least 4 pouches, not the 2 pack in this Amazon listing. BUT THEY DO WORK. And, quickly. So, you can install them today, and your trailer will smell clean and sanitized tomorrow with a hint of chlorine scent. Beats smelling poop.
Amazon.com: Star brite NosGUARD SG Mold/Mildew Odor Control System (2 Pack): Sports & Outdoors