I am concerned about making up my internal solution, aliquoting into 500ul then freezing. Is this the usual method people use?
yes, except that my aliquots are 1 ml
Why would you not recommend storing the solution in the fridge?
If the internal solution conatins BSA or other protein, it will be degraded at RT or refrigerator as well as may even lead to microbial growth. So it is not stored in fridge but freezed.
Freezing is necessary if you are adding ATP and GTP to your aliquots to prevent ATP/GTP degradation.