water tank

There are any number of tank mfrs / suppliers out there.  Best thing to do is to get the old tank out and get measurements of it to compare.

Here's my suggestions:

1.  If there's room, get a tank with a pick up sump so you can get the absolute last drop out of the tank.  I know that my ~54 gal tank only gives me about 50, at best, due to the pickup being in the =side= of the tank, so can't suck up that last 1/2 to 3/4" off the bottom.

2.  Again, if you have any room, see if you can get a tank that's a few inches longer or wider.  When you run volume calcs, it's amazing at how little it takes to pick up a few extra gallons of capacity.  Yeah, you might have to re-engineer the brackets due to size or =weight= considerations, but the tradeoff for a bit more water, is usually  way positive in the long run.

3.  If you have room =above= the tank, run your vent line out the top, instead of the side.  Again, you'll be able to get more in the tank before it overflows.  Down side is that you =really= need to watch where the vent goes to prevent siphoning.  My rig was siphoning when new, badly, and I had it modified under warranty.  They ran the vent lines up, and over, the main frame.  My first few trips I was seeing a water trail behind me and that's what I narrowed it down, to.  One of the reasons I wish my rig had a gravity fill, with the vent right next to the inlet.