Is that one of those "Pick and Pluck" cases, where the foam is pre-scored in little square columns, and you just remove what you need? (I ask this because of the square-ness of the openings in the case lid, which could have stemmed either from a careful cutting job on your part, or pre-scored foam on their part.)
If so, I'd not trust it, as the weight of a large wood instrument is too way much for the foam in that instance. I've tried the system for some relatively heavy sound equipment, and the weight of the components combined with the vibration of motor travel was all that it took to split the case foam apart. It didn't happen at first, but after a year of hauling things about, it slowly but surely took the foam apart.
Heavy joints (like either of the two in the case of a wooden bass) are about as bad as sound junk. And, unlike sound junk (which is meant to take the abuse that vocalist routinely dish out - I almost killed one vocalist who dropped his cordless mike on the stage (a la rock musician style) after a particularly strong performance, but he assured me that Shure had taken that into account - he also didn't offer to replace the dented microphone screen that he caused), those keys and touch pieces on the bass are a lot more fragile.
If it is cut from the solid, then I would modify my statement to the effect that, as long as certain areas are cut clear (so that the keys are not restrained in those instances), the foam cavity approach will work just fine. The trick is to study the case as designed (allowing for damage to same, and figuring out what is missing), and then design the holes in the new case accordingly.
And, even then things can go wrong. A story covering a long-standing problem:
I had troubles with my low F/clarinet C key work on my bass for thirty years. I would treat the thing like an english horn, carefully storing the joints each and every time, and guarding it against any contact when in use or on a stand. Yet, it would invariably go out after a week or two.
One time, I had it adjusted and loaded in the case by Marvin at Saint Louis Woodwind and Brasswind, and then drove to a job in Kansas City. After carefully removing the horn from the case and putting it together, bingo! there was a leak in the F/C key work. It was at that point that I first suspected the case, and not careless handling on my part. (I would never suspect Marvin of careless anything save his far right wing politics.)
After finishing the job there in Kansas, I took the time to study the case more closely, and then learned that there was a small anomaly in the way that the lower joint fit into the casework. A combination of a loose cushion in the top with a contour in the Plywood cutout in the lower half allowed the joint to (when the case was "vertical") to drop "above" the Plywood portion of the case. Then, when the case was placed "horizontal", the keys (key cups) on the lower section would "hang up" on the Plywood, rather than be carefully contained in the hanging fabric below the cutout.
Rinse and repeat a few times, combined with vibration and "un-cushioned" hits in the trunk of a car, and there's your slight bending that caused the leaks. But, if yo didn't look carefully at the case, you would never have noticed it.
Upon return to the Gateway City, we collectively disassembled the case structure and found - surprise, surprise! - that whoever did the cutout work on the Plywood at Selmer's case fabrication facility had not cut to the lines inscribed on the piece, leaving a "lip" that did the catching and holding. Thanks, Selmer...
Once the "lip" was carefully jig sawed off and the fabric (thirty years old fabric, mind you) was rehung, no more problem.
Obviously, Selmer's cases are not manufactured to the same high standards as their instruments. After this occurred, I had a number of changes made to the cases for my horns, and in each case (pun intended), the modifications corrected long standing issues with the instruments concerned. In one case (for my Puerto Rican full Boehm horn), a case had a blown plastic mould holding the joints, and the plastic had failed, leaving the long levers on the lower joint bearing against a protrusion. Not as critical as the bass problem above, but still needing to be addressed.
The best cases that I've ever had have been the Yamaha baritone cases. I've owned two, the original one with the wheels, and the replacement purchased through eBay (from someone who dumped the case (which is heavy as hell) to use a gig bag (dumb move, at least in my opinion). I've had a horn dropped off of the back of a truck in a Yamaha case, and the horn sailed through the ordeal without a glitch. Hard to believe, but true.