Yes, a wood frame with liner just like most others have done.
The more gallons the more stable it is, although that is not really why. I got the 125g with plans to use as a tank but the reseal went sour so a sump it is. Plus it will hold a crap ton of Bio Media, Heater(s), and so on with no issues. Plus it will add some more volume to the total system making it more stable. I will likely drill it about 1/2 way up though so maybe 50g will be in it at the most at any given time. I don't want it to heavy since it will be sitting over the pond and on a stand that will only be supported on the sides since I don't want a support sitting in the pond obviously.
The more gallons the more stable it is, although that is not really why. I got the 125g with plans to use as a tank but the reseal went sour so a sump it is. Plus it will hold a crap ton of Bio Media, Heater(s), and so on with no issues. Plus it will add some more volume to the total system making it more stable. I will likely drill it about 1/2 way up though so maybe 50g will be in it at the most at any given time. I don't want it to heavy since it will be sitting over the pond and on a stand that will only be supported on the sides since I don't want a support sitting in the pond obviously.