Here's a blow by blow, if you want to do a fix. We've had one tank replaced by the factory, and both now bulge to some extent, but not as much as the first had. The condition appears stable. Here's what we've done, and it seems to be a good fix. I'll post some photos later:
1: Get both tanks essentially empty, either by running the motor, or by siphoning. If siphoning, do so into your car's tank, rather than 5 gallon gas cans, so you don't have to worry about overflow onto the driveway. REMEMBER, the fuel-air mixture which remains in the tanks is highly explosive, and, if ignited by static or any other means, will put you in a nursing home or grave. Don't get careless. SEE THE NOTE AT THE END OF THIS ITEM BEFORE YOU EMPTY THE TANKS.
2: unscrew the clamp which holds the strap to the forward vertical panel, remembering that there is probably considerable tension on the strap because of distortion of the tank. I've not had any luck getting the strap d-rings to release when under high tension, but you sure can give it a try.
3: unscrew the fuel tank retainers (front and side) from the deck, clean out the holes as best you can after making sure they're dry, and plug with 3m 4200, being sure to avoid air pockets. Suggest using a wood match stick or toothpick to press up and down through the 4200 to release the air, then give it some more 4200, and repeat until no more air escapes. Wipe flush, but don't worry about it being too pretty, since nothing will show, anyway.
4: push each fuel tank securely against the side and rear of the boat, and mark the outline around the front and inside. This is important because a near empty fuel tank, if not restrained, will move around without your knowing, and you'll end up securing it in the wrong spot. It doesn't hurt to do this on a hot day, so the tanks have undergone whatever heat expansion they're inclined to do. Make sure there isn't debris around the tank which prevents you from getting a good fit.
5: clean up the front retaining panel and screws (or just replace the screws), and if necessary, reconfigure the lower strip. On ours the vertical panel was 1/2 inch starboard, and the horizontal 1x1 starboard (give or take), screwed to the 1/2 inch from the rear. I reversed the screws, so that the 1x1 is secured from the front. That way, I can separate the panel from the 1x1 and pull the fuel tank, without disturbing the 1x1, and it's screws which attach to the deck of the boat. This reversal results in some degradation of the holding power of the screws which secure the 1x1 to the 1/2, but you can just add a few more, and be pretty close to the initial strength. I don't think step 5 is critical, so if your 1x1 or equivalent is something other than starboard, don't mess with it.
6: put the front retainers back in place, vertical against the front of the tanks, and be sure that the the clamp and any retainers which attach the straps slightly clears the top of the tank, rather than resting up against the front side. If necessary, redrill the strap retaining holes through the 1/2 inch starboard, and plug the old ones with 4200. Then, put the front panel in place, mark the holes to be drilled in the floor, and mask along the exposed sides between the 1x1 and deck. I prefer to make a small (1/8) inch pilot hole, and then drill to final size, which should allow the mounting screws to have enough bite in the fiberglass to make a firm fit, but not so much that you delaminate the glass. I always countersink slightly to prevent delamination. Watch out here, because if you sink either drill bit too far, you'll go through the balsa, and come out through the bottom of the boat. Use a probe wire after the first 1/8 inch hole, and probe down through the balsa until you hit the top of the underside, mark the depth, and be carefull drilling the rest of your holes, because the depth could vary. If the drill motor prevents you from getting totally perpendicular to the deck, just do the best you can, and get the screws to feed essentially perpendicular with a firm hand on the screwdriver, and a little patience. Practice on one screw, before drilling the holes for the rest, and make any adjustments in drill size that are necessary to get the final fit you want. I like to use a dental tool to open up a little cavity in the top of the balsa. Insert the mounting screws slightly in the holes to cut threads in the fiberglass and push out any balsa to the depth the screw will go when in place, then unscrew, and pack the holes with 4200. Lay a bead of 4200 where the 1x1 will rest on the deck, put the starboard in place, shoot some 4200 in the holes through the starboard, then insert the screws. Since my holes were oversized from a prior attempt, I used bolts, which are secured in place totally by the 4200, and don't actually contact the fiberglass. I don't like to be too careful cleaning up 4200 around screw or bolt heads, and just leave a bead showing to be extra sure that I've got a water tight seal. Reattach and tension the strap after the 4200 has cured.
7: I trashed the 1x1 starboard side retainer strips because they trapped water in an area where I want it to move to the sump at the drain plug, and not be forever trying to work it's way into the screw holes where the 1x1 is secured to the deck. Instead, I bought an aluminum angle piece at Lowes or HDepot, cut it into sections, and used two sections on each side to secure the tanks in place laterally. Again, mask, drill, countersink, etc. Given the forces which are generated when masses such as full fuel tanks try to slide back and forth in a boat, I added a marine ply thrust block, which transfers the force from one tank to the other, without affecting the aluminum retainers. Some pretty rough water hasn't made a dent on this setup. Except for the front 1/2 panel, which has considerable give, I was careful to restrain the tanks, be it with aluminum or a thrust block, only along the edges. That's where the deflection from loading with fuel, heat changes, etc. will be the least. I wouldn't add a thrust block or any other retainer which applied force to the center of a fuel tank side, because if it (or they) are inclined to deflect there, you are going to be dealing with forces which could rupture one or both tanks, or damage the side of the boat.
ONE NOTE: Before doing any of this, you should find out whether your tanks change shape when they're full of gas, hot, cold, etc. If you have considerable change, you can make some compensations during your work. The last thing you want to do is to go through this effort with empty tanks, thinking you've solved the problem, only to discover that you now have well secured tanks which distort when filled, and push everything you did all out of shape.
Both my "new" tanks are bulged about an inch on all sides. I'm really puzzled as to why some do and some don't. Any thoughts.
The boat tanks not noticeably so.