A proper truck tire gauge, and the corresponding inflation tool (and valve cap tool) can make extensions unnecessary, properly supported long stems make the job much easier. I've actually done OK the past 14 yearsusing armored flexible extensions on the inner duals, and screwing temporary metal extensions onto the short metal stems on the outers and front, for checking and filling. All this was made easier when I pulled off the razor-sharp stainless steel wheel liners and stored them in my garage.
I don't check and fill monthly, I check before I drive, every day I drive.