It sounds like the odor you notice is only when you dump the tank, and not inside the camper. From your picture it looks like you are setup like a seasonal on some land of yours. The TT is stationary, and is not hauled home.
My guess is you have a build up of sludge, that is decaying. I do not recommend bleach, it will kill any good bacteria.
Do you normally keep the grey tank waste valve open, or is it closed until you need to dump? If you dump periodically, do you make sure the tank is 100% drained before closing the valve? Or by the method of it is drained good enough (mostly empty)? After emptying the tank, do you add any FW into the tank or treatments? Is the tank fully dry between weeks?
Periodically I add some liquid fabric softener, other people will add Water Softener. They both do the same thing. It will change the surface tension of the water, so the water is "Wetter" and can pernitrate into the sludge. Only time I ever fully drain my waste tanks is in the fall when I winterize. Otherwise I always try to keep a few gallons of water in each of them. Since keeping a little water, I have eliminated the odor. Typically only time I get odor, is in the spring when the tank first gets wet, and it lingers for a couple weeks.
If it was me, I think I would add about a 1/2 to 1 cup of liquid fabric softener in a 5 gallon bucket, pour down the drain, when you get to camp. Let the tank fill up. At the end of the weekend, if you did not need to drain the tank, filler all they way up, and leave for the week in the tank. Next week drain it, when you get there. Add another 4-5 gallons of water and more liquid fabric softener. May need to do this a few times.
If you pulled the camper home after camping, I would go about it slightly differently. As I drive home with 4 gallons of water and the fabric softener, it will slosh and wash the tank. But your stationary, so you need to encourage the sludge on the walls to settle down and drain out of the tank. Hence keeping the tank wet, with wetter water.