It's nice to have a big holding tank.
I fitted a polyethylene holding tank of about 150 litres to Boracay. Used 2 x 1/4" breathers and no worries so far. Last about 10 or so days with just 2.
The biggest problem that I have encountered is that the top of the holding tank is about 1m above the pan and it takes a bit of work to empty the pan.
On the other hand that puts the top of the holding tank just below the deck
and makes it easy to empty.
If I was doing it again I'd use a smaller tank below the sole and empty it to the larger tank with a macerator pump as it became full. Some sort of gauge is a good idea. I used a dip stick and it's not something one wants to do all the time.