Wendy suggested 5 to 5.5u every 8 hours if you were going to stick with 3x/day. That would mean a total of 15 - 16.5u a day. Therefore, if you are shooting twice a day, I’d start at 7.5u twice a day and absolutely no less than 7u twice a day. Of course, it helps us more if the SS is up-to-date so trying to get all the BGs entered to today would be extremely beneficial.
Instead of Saran Wrap, I use to stick a large spoon under Gracie’s bottom as she squatted and it always worked. My vet also has small plastic trays to slip under the kitties’ bottoms as they squat. You could even use the lid to a plastic container that something like butter or sour cream comes in as long as it is spotlessly clean.
If you can catch him before he pees first thing in the morning, if you put him in the box, perhaps you can get a sample. This was always the easiest way for me to get urine from Gracie without having to watch her all day to see when she went to the box. She would always “pee on demand” first thing in the morning.