The only proviso on that is that not all LTVAs are created equal and so some of us who do not have commercially manufactured RVs are restricted as to which LTVAs we can use.
My van does not have the required 10 gallon black water holding tank and so is restricted from some LTVAs and required to be parked within 500' of a bathroom facility in others. I chose instead to install a C-Head marine toilet. These toilets were not taken into consideration when the regulations were put in place.
Holtville is an example of this. The only washroom facilities are in the day use area. As such, my van does not qualify to stay on LTVA grounds. Fortunately for me, there is free dispersed camping right behind the south LTVA area that I can use.
Also, some LTVAs have more facilities than others. Some have dump stations, some don't. Same goes for water. Check the on line listings so that you know in advance what each LTVA has available.