Equites sagittarii (late 2nd century)

[jho]

On Intercisa see here:

FRE

I do not think that camps for archer units were different from those of other units but you may want to google the following short list of alae for their respective forts:

Ala Celerum
Ala I Hamiorum Syrorum
Ala I Augusta Ituraeorum
Ala Parthorum et Araborum
Ala I Sagitariorum Surorum milliaria
Ala I Thracum veteranorum
Ala III Augusta Thracum sagittariorum

You should be aware that gravestones show that "generic" cavalry units may have also included archers (e.g. the equites singulares (e.g. at Mainz), the famous Batavian who crossed the Danube before hitting an arrow with a second one, and the trooper of ala Scubulorum mentioned above).

Finally, I have not read but this thesis which is available online may also be helpful:

the horse archers of the Roman Imperial Army