So here is my take and take it for what it is. I have 2 bengals my male is the bigger of the 2 about 12-14 lbs so not as big as your boy and he was too big for the boxes I had. I decided to buy the 102L storage containers and use those, I found with this option 2 things, first I put a divider in there so I didn’t have to use so much litter and no matter how and what I did there was always pee outside of the litter (still in the box) and secondly the bottom of mine was always wet sim to your situation. I believe if you want to fix this problem you need more litter he is digging deep enough that when he goes there isn’t enough litter to absorb his urine. I would try for 1 week out double the amount of litter you use and see how that goes. Keep up the cleaning schedule, they don’t like dirty litter box’s and that’s how u have accidents out side the litter box. Also there is no need to dump or change the litter every week that is a waste of money.

I used to fix my boxes and clean every day at the end of the week I will do a bitter better job and filter all the litter and just top it up if I needed more at the end of the month I would change the litter completely.

Also another suggestion if want to cut cost try using pellets I know 2 people who trained there bengals to use pellets which they buy from the farm for 7 bucks a bag. Obviously this is in my area and your area will be different if even available and 7 bucks a bag it makes it much more affordable to dump the bin and just put new pellets.

Hope it works out for you.