I'm not a fan of bladders for waste holding
"Too small" is relative. I was on a "no discharge" lake for more than 20 years with only an 18 gallon tank...it was adequate for us for as much as a 3 day weekend. But there were only two of us...it might not have been big enough for a family of four.
So...let's find out what you actually do need (or think you do). Toilet--manual or electric? How many people? How long do you thiink you should be able to last between pumpouts? Where do you spend most of your time...hugging the shore inside 3 miles, or out in the Gulf?