If this is your first trip, and you are new to RVing; suggest you drain black and gray water tanks, if possible. Then, purchase and add Thetford "Campa-Chem Holding Tank Deodorant", following the instructions. This product is frequently provided with new RVs and porta-potties, and it is very likely the "blue water" you see in airline-type recirculating toilets. (Make sure the bottle contains formaldehyde; as there is a "green" version that does not, which doesn't work as well.)
You can experiment with other products later, including the Geo Method, to see what works for you; but this is a good place to start on odor control. It is probably the most effective product/method, especially in the summer heat. Thetford and other brands of toilet chemicals are widely available, including WalMart and RV/Marine parts stores. I think WalMart has the 32 ounce bottle priced below $5.
Note: This product contains formaldehyde and can permanently stain blue whatever it touches, including your hands, clothing and trailer surfaces (flooring, walls, etc.). So, be careful where it splashes; and keep the lid to avoid spilling, in case you knock it over.