Boosting outside means boosting between the nappy and the cover
You can use a small hemp trifold and put it on the area where it's prone to wet the most, then put a cover on.
He may start to change his wee habit. I find that between 12 months to 16 months is the heaviest period, especially night time. Mine was drinking through the night though, but when she passed that period, her weeing seems to be lighter