You can make it stronger, i do 10 mg/ml personally. Dosed with a 100 unit oral syringe. Just mix the powder with the pg, take a syringe or something and stir it around(syringe is good to mix with via sucking/pushing solution out). Let the solution settle, break up any clumps, repeat blending until you get a uniform solution.
Heat isn't necessary, but a hot water bath with hot tap water will speed it up