Awesome info from Brian, love having direct access to the designer like this!
Todd, I have a few strong recommendations - you're doing a great job, hopefully this helps:
1. Eliminate the small flat at the bottom of your tank and just make it a V-shape. Whoever builds your tanks will bend the tank with a brake, and saving them a bend will be helpful and will have little impact on volume or clearance and will likely save you a bit of cash and save the builder some headache.
2. Raise your deck at least 2 1/2" above the top of the stringers. This has many benefits and only one small disadvantage: Benefits are your tanks can go to the top of the stringers (more volume) and there is still plenty room to run fill, vent, and pickup hoses/fittings without having to cut the stringers; This way the top plate of the tanks can be extended as I did with mine to support the tanks on top of the stringers, keeping the bilge clear - no need to place struts on the bottom of the boat to support the tanks, which clutters up the bilge and is a LOT of work comparatively (Dave in Homer and I both did this); this deck height also puts the scuppers above the water line adequately so water does not normally come on board when you're standing at the transom. Disadvantages are that your clearance into the cabin is reduced compared to inside because of the roof extension (just account for this when deciding cabin height).
3. Use 3/16 aluminum - it is plenty strong, 1/4" is way overkill and just adds unnecessary weight
4. Wherever the tank lands on support, bed the ENTIRE area with sealant so zero water/air can penetrate this area. That will prevent pit corrosion.
5. Leave about 3/4" clearance all around for air to circulate
6. Strongly consider 2" or bigger gimble holes at the bottom of all your bulkheads so you can really ventilate bilge fumes out of the boat through passive or active means (you could do a dorado vent in front and back, or install an explosion proof bilge blower). Also, have a way to plug the forward bulkhead so fumes do not go into your cabin, and have the rest of the floor over the bilge completely sealed off, at least inside the cabin. When I finally figured that out, my cabin became completely fume free and it's wonderful.
7. Make darn sure your fuel fill and vents are at least 6" apart, and 8" or more is better. My aft tank has them about 1 1/2" apart and I get fuel out the vent, so I get to cut into my deck this spring and install a new vent tap which is going to be touchy work. While you're at it, put a vent on both forward and aft of the tank so no matter how your boat is sitting on trailer or water, it will vent properly, especially as it's getting full
8. Have the tank fabricator give you a tab on both tanks tapped for a #10 screw for a bonding wire
9. Place the tank pickups in the aft end of the tanks so you get all the fuel - you're always slightly nose up when running.
10. Fight for every gallon you can get from each tank. You never have enough fuel. I already wish I had more. With the 250, plan on 3 nmpg, no more. 2.8 if you like to run at 30 knots.
Some of the above I got right and am super pleased, a few I missed and had to do a lot of painful rework. Fuel tanks are important, aluminum tanks DO fail with in a few years if not done correctly, and there's surprisingly little good advice available online. Hopefully you can find someone knowledgeable to fab the tanks for you. Have fun and good luck!