If you are in La Quinta, your weather is similar to Phoenix.
We have tried about every kind of deodorant, including "The Geo Method", "green" chemicals and various marine toilet products. However, Thetford Campa Chem with formaldehyde (the blue stuff) is the only thing that seems to work in extreme desert heat. In cooler weather, most of the other products provide satisfactory results; but in the summer, that's all we use.
Campa Chem Liquid Holding Tank Deodorant, 64-ounce: Other Patio & Garden : Walmart.com
Depending on the size of your holding tank, 4 ounces will usually work in cooler months. However, in 110 degree heat, the standard dose of toilet chemicals is usually insufficient to control odors. So, during the summer, I'd double that to 8 ounces (1 cup). Then, as your tank fills, if bad odors return and you are unable to dump, add another 8 ounces.
Note: This is the same stuff that the airlines, trains and buses use in their toilets. And, despite what most people think, this formula is biodegradable. Also, be careful handling this chemical; as it permanently stains anything it touches blue (except the toilet), including walls, floors, and your hands!